Apparatus for fiber reinforced additive manufacturing

ABSTRACT

Various embodiments related to three dimensional printers, and reinforced filaments, and their methods of use are described. In one embodiment, a void free reinforced filament is fed into an conduit nozzle. The reinforced filament includes a core, which may be continuous or semi-continuous, and a matrix material surrounding the core. The reinforced filament is heated to a temperature greater than a melting temperature of the matrix material and less than a melting temperature of the core prior to applying the filament from the conduit nozzle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S.provisional application Ser. Nos. 61/804,235, filed Mar. 22, 2013;61/815,531, filed Apr. 24, 2013; 61/831,600, filed Jun. 5, 2013;61/847,113, filed Jul. 17, 2013; 61/878,029, filed Sep. 15, 2013;61/880,129, filed Sep. 19, 2013; 61/881,946, filed Sep. 24, 2013;61/883,440, filed Sep. 27, 2013; 61/902,256, filed Nov. 10, 2013, and61/907,431, filed Nov. 22, 2013, the disclosures of which are hereinincorporated by reference in their entirety; and is a continuation inpart of each of U.S. patent application Ser. No. 14/222,318, filed Mar.21, 2014 and Ser. No. 14/297,437, filed Jun. 5, 2014, the disclosures ofwhich are herein incorporated by reference in their entirety.

FIELD

Aspects relate to three dimensional printing.

BACKGROUND

“Three dimensional printing” as an art includes various methods such asStereolithography (SLA) and Fused Filament Fabrication (FFF). SLAproduces high-resolution parts, typically not durable or UV-stable, andis used for proof-of-concept work; while FFF extrudes through a nozzlesuccessive filament beads of ABS or a similar polymer.

“Composite Lay-up” is not conventionally related to three dimensionalprinting. In this art, preimpregnated (“prepreg”) composite sheets offabric are impregnated with a resin binder into two-dimensionalpatterns. One or more of the individual sheets are then layered into amold and heated to liquefy the binding resin and cure the final part.

“Composite Filament Winding” is also not conventionally related to threedimensional printing. In this art, sticky “tows” including multiplethousands of individual carbon strands are wound around a custom mandrelto form a rotationally symmetric part. Filament winding is typicallylimited to convex shapes due to the taut filaments “bridging” anyconcave shape.

There is no commercial or experimental three dimensional “printing”technique which provides the benefits of composite lay-up, or compositefilament winding.

SUMMARY

According to a first embodiment and/or aspect of the present invention,one combination of steps and/or a three dimensional printer employing asubset or superset of such steps for additive manufacturing of a partincludes supplying an unmelted void free fiber reinforced compositefilament including one or more axial fiber strands extending within amatrix material of the filament, having no substantial air gaps withinthe matrix material. The unmelted composite filament is fed at a feedrate along a clearance fit zone that prevents buckling of the filamentuntil the filament reaches a buckling section (i.e., at a terminal andof the conduit nozzle, opposing the part, optionally with a clearancebetween the conduit nozzle end and the part of a filament diameter orless) of the conduit nozzle. The filament is heated to a temperaturegreater than a melting temperature of the matrix material to melt thematrix material interstitially within the filament, in particular in atransverse pressure zone. A ironing force is applied to the meltedmatrix material and the one or more axial fiber strands of the fiberreinforced composite filament with an ironing lip as the fiberreinforced composite filament is deposited in bonded ranks to the part.In this case, the ironing lip is translated adjacent to the part at aprinting rate that maintains a neutral to positive tension in the fiberreinforced composite filament between the ironing lip and the part, thisneutral-to-positive (i.e., from no tension to some tension) tensionbeing less than that necessary to separate a bonded rank from the part.

According to a second embodiment and/or aspect of the present invention,an additional or alternative combination of steps and/or a threedimensional printer employing a subset or superset of such steps foradditive manufacturing of a part includes the above-mentioned supplyingstep, and feeding the fiber reinforced composite filament at a feedrate. The filament is similarly heated, in particular in a transversepressure zone. The melted matrix material and the at least one axialfiber strand of the composite filament are threaded (e.g., through aheated print head, and in an unmelted state) to contact the part in atransverse pressure zone. This transverse pressure zone is translatedrelative to and adjacent to the part at a printing rate to bring an endof the filament (including the fiber and the matrix) to a meltingposition. The end of the filament may optionally buckle or bend to reachthis position. At the melting position, the matrix material is meltedinterstitially within the filament.

According to a third embodiment and/or aspect of the present invention,a three-dimensional printer, and or a subset or superset of method stepscarried out by such a printer, for additive manufacturing of a partincludes a fiber composite filament supply (e.g., a spool of filament,or a magazine of discrete filament segments) of unmelted void free fiberreinforced composite filament including one or more axial fiber strandsextending within a matrix material of the filament, having nosubstantial air gaps within the matrix material. One or more linear feedmechanisms (e.g., a driven frictional rollers or conveyors, a feedingtrack, gravity, hydraulic or other pressure, etc., optionally withincluded slip clutch or one-way bearing to permit speed differentialbetween material feed speed and printing speed) advances unmeltedcomposite filament a feed rate, optionally along a clearance fit channel(e.g., a tube, a conduit, guide a channel within a solid part, conveyorrollers or balls) which guides the filament along a path or trajectoryand/or prevents buckling of the filament. A print head may include (alloptional and/or alternatives) elements of a heater and/or hot zoneand/or hot cavity, one or more filament guides, a cold feed zone and/orcooler, and/or a reshaping lip, pressing tip, ironing tip, and/orironing plate, and/or linear and/or rotational actuators to move theprint head in any of X, Y, Z, directions and/or additionally in one tothree rotational degrees of freedom.

In this third embodiment/aspect and optionally other embodiments/aspectsof the invention, a build platen may include a build surface, and mayinclude one or more linear actuators to move the build platen in any ofX, Y, Z, directions and/or additionally in one to three rotationaldegrees of freedom. The heater (e.g., a radiant heater, an inductiveheater, a hot air jet or fluid jet, a resistance heater, application ofbeamed or radiant electromagnetic radiation, optionally heating theironing tip) heats the filament, and in particular the matrix material,to a temperature greater than a melting temperature of the matrixmaterial (to melt the matrix material around a single fiber, or in thecase of multiple strands, interstitially among the strands within thefilament). The linear actuators and/or rotational actuators of the printhead and/or build platen may each solely and/or in cooperation define aprinting rate, which is the velocity at which a bonded rank is formed. Acontroller optionally monitors the temperature of the heater, of thefilament, and/or and energy consumed by the heater via sensors.

In this third embodiment/aspect and optionally other embodiments/aspectsof the invention, the feed mechanism, clearance fit channel, linear orrotational actuators of the build platen and/or the linear androtational actuators, guides, hot cavity, and/or reshaping or ironinglip or tip of the print head may optionally cooperate (any combinationor permutation thereof or all) as a transverse pressure zone thatpresses and/or melts filaments onto the build platen or into the partbeing printed. Optionally, the linear and rotational actuators of theprint head and/or build platen, and/or one or more linear feedmechanisms may be controlled by a controller monitoring force,displacement, and/or velocity sensors to apply a compressive force alongthe axial strands (e.g., tangentially to a feed roller diameter) of thefilament and/or apply a reaction force from the build platen or partbeing printed to press melted matrix filaments against the build platenor against or into previous layers of the part to form bonded ranks(i.e., substantially rectangular ranks adhered to substantially flatsurfaces below and to one side thereof).

In this third embodiment/aspect and optionally other embodiments/aspectsof the invention, fully optionally in addition or the alternative, thelinear and rotational actuators of the print head and/or build platen,and/or one or more linear feed mechanisms may be controlled by acontroller monitoring force, displacement, and/or velocity sensors toapply a transverse, sideways, downwards, ironing and/or ironing force(optionally using a surface of or adjacent the print head, which may bea reshaping and/or ironing lip, tip, or plate) to the side of the meltedmatrix filament to press and/or iron the melted matrix filaments againstthe build platen or against or into previous layers of the part to formbonded ranks. Fully optionally in addition or the alternative, thelinear and rotational actuators of the print head and/or build platen,and/or one or more linear feed mechanisms may be controlled by acontroller monitoring force, displacement, and/or velocity sensors toapply a neutral to positive tension force through the strand andunmelted matrix of the filament and/or between the build platen,previously deposited bonded ranks and the print head or feedingmechanism(s) (optionally using a surface of or adjacent the print head,which may be a reshaping and/or ironing lip, tip, or plate, and furtheroptionally using interior surfaces of the print head or guides, and/orfeeding mechanism clutches, slips, motor drive, idling, motor internalresistance, and/or small resistance currents) adjacent to the part at aprinting rate that maintains neutral to positive tension in the fiberreinforced composite filament between the reshaping lip and the part.This tension force is optionally a neutral to positive tension forceless than that necessary to separate a bonded rank from the part forsustained formation of bonded ranks, and further optionally and/or inthe alternative, may be sufficient to separate or sever a filament witha discontinuous internal fiber connected by melted matrix to the printhead.

In this third embodiment/aspect and optionally other embodiments/aspectsof the invention, including the first and second embodiment/aspectsthereof, the linear and rotational actuators of the print head and/orbuild platen, and/or one or more linear feed mechanisms may becontrolled by a controller monitoring force, displacement, and/orvelocity sensors to apply a transverse, sideways, downwards, reshapingand/or ironing force (optionally using a surface of or adjacent theprint head, which may be a reshaping and/or ironing lip, tip, or plate)to generate a different balance of forces within the printer, filament,and part in different printing phases (e.g., threading phases versusprinting phases). For example, in one embodiment or aspect of theinvention, the linear and rotational actuators of the print head and/orbuild platen, and/or one or more linear feed mechanisms may becontrolled by a controller monitoring force, displacement, and/orvelocity sensors to apply a transverse, sideways, downwards, reshapingand/or ironing force (optionally using a surface of or adjacent theprint head, which may be a reshaping and/or ironing lip, tip, or plate)may apply bonded ranks primarily via lateral pressing and axial tensionin a continuous printing phase of applying bonded ranks, and primarilyvia lateral pressing and axial compression in a threading orinitialization phase.

In a fourth embodiment and/or aspect of the present invention, athree-dimensional printer, and or a subset or superset of method stepscarried out by such a printer, for additive manufacturing of a partincludes a fiber composite filament supply of unmelted fiber reinforcedcomposite filament including one or more inelastic axial fiber strandsextending within a matrix material of the filament. A movable buildplaten for supports the part. A print head opposes the build platen andincludes a composite filament ironing tip and a heater that heats thecomposite filament ironing tip above a melting temperature of the matrixmaterial. A plurality of printing actuators move the print head and thebuild platen relative to one another in three degrees of freedom, and afilament drive that drives the unmelted fiber reinforced compositefilament, and the inelastic fiber strands embedded within, into theprint head at a linear feed rate. A cold feed zone positioned betweenthe filament drive and the ironing tip is maintained below a meltingtemperature of the matrix material. A controller operatively connectedto the heater, the filament drive and the printing actuators executesinstructions which cause the filament drive to hold an unattachedterminal end of the composite filament in the cold feed zone between thefilament drive and the ironing tip. The controller may optionallyexecute further instructions to cause the attached operative elements tocarry out the functions described herein below.

In this fourth embodiment/aspect and optionally otherembodiments/aspects of the invention (“other embodiments/aspects”including without limitation the first, second, third and fourthembodiment/aspects thereof), the filament drive to advances theunattached terminal end of the composite filament through the print headand to the heated composite filament ironing tip without stopping, suchthat the unattached terminal end advances at least at the currentfeeding rate as it passes through locations having a temperaturesufficient to melt the matrix material of the filament. Fullyoptionally, the filament drive may advance the unattached terminal endof the composite filament through the print head and to the heatedcomposite filament ironing tip at a speed sufficient to prevent theunattached terminal end from receiving sufficient heat transfer toadhere to interior walls of the print head adjacent the compositefilament ironing tip.

Additionally and/or optionally in this fourth embodiment/aspect andoptionally other embodiments/aspects of the invention, the actuators tobegin moving the print head and the build platen relative to one anotherin at least one degree of freedom substantially at the moment thefilament drive advances the unattached terminal end of the compositefilament to the heated composite filament ironing tip. Alternatively, orin addition, the filament drive advances until the terminal end and atleast a portion of the one or more inelastic axial fiber strands areanchored within a part on the build platen.

Additionally and/or optionally in this fourth embodiment/aspect andoptionally other embodiments/aspects of the invention, a cutter ispositioned between the filament drive and the ironing tip, which seversthe unmelted fiber reinforced composite filament within the cold feedzone. Subsequent to severing the unmelted fiber reinforced compositefilament, the actuators may drag remaining unmelted fiber reinforcedcomposite filament from the print head through the cold feed zone andthe composite filament ironing tip. Alternatively, or in addition,subsequent to severing the unmelted fiber reinforced composite filament,the filament drive may hold the unattached terminal end of the unmeltedfiber reinforced composite filament in the cold feed zone adjacent thecutter. Alternatively, or in addition, the cutter may be positionedbetween the filament drive and the ironing tip, and severs the unmeltedfiber reinforced composite filament prior to holding the unattachedterminal end of the unmelted fiber reinforced composite filament in thecold feed zone between the filament drive and the ironing tip.Alternatively, or in addition, the cutter has a blade having a thicknessof less than the diameter of the unmelted fiber reinforced compositefilament between an entrance guide tube and an exit guide tube, thedistance between the entrance and the exit guide tubes and the thicknessof the blade are equal to or less than the diameter of the unmeltedfiber reinforced composite filament.

Additionally and/or optionally in this fourth embodiment/aspect andoptionally other embodiments/aspects of the invention, a clutch permitsthe filament drive to slip to accommodate a difference in the printingrate and the feeding rate. Fully optionally alternatively or inaddition, a clearance fit channel within the cold feed zone has an innerdiameter between 1½ and 2½ times the diameter of the unmelted fiberreinforced composite filament, and guides the filament along a path ortrajectory and/or prevents buckling of the filament. Fully optionallyalternatively or in addition, an interior diameter of the print headbetween the clearance fit channel and the composite filament ironing tipis from two to six times the diameter of the unmelted fiber reinforcedcomposite filament, sufficient to prevent the unattached terminal endfrom receiving sufficient heat transfer to adhere to interior walls ofthe print head adjacent the composite filament ironing tip.

Additionally and/or optionally in this fourth embodiment/aspect andoptionally other embodiments/aspects of the invention, the printingactuators and the filament drive cooperate to maintain a transversepressure zone that both presses and melts fiber reinforced compositefilament to form the part on the build platen as the build platen andprinthead are moved relative to one another; and or to cooperate toapply a compressive force along the inelastic axial strands of thefilament; and/or to apply an ironing force, using a surface of theheated composite filament ironing tip, to the side of the melted matrixfilament to form the part on the build platen; and/or to apply a neutralto positive tension force along the embedded inelastic fiber and betweena part anchoring an embedded inelastic fiber and the heated compositefilament ironing tip.

Additionally and/or optionally in this fourth embodiment/aspect andoptionally other embodiments/aspects of the invention, the printingactuators and the filament drive substantially simultaneously pause, thecutter then severs the unmelted fiber reinforced composite filamentduring said pause, and the print head and the build platen then moverelative to one another along at least one degree of freedom for atleast a runout distance (measured between the cutter and the ironingtip) to complete bonding the remainder of the fiber reinforced compositefilament.

Additionally and/or optionally in this fourth embodiment/aspect andoptionally other embodiments/aspects of the invention, the filamentdrive advances the unmelted fiber reinforced composite filament by therunout distance before causing the printing actuators and the filamentdrive to substantially simultaneously drive along at least one commondegree of freedom at a substantially common speed of advance of theinelastic axial fiber strands within the fiber reinforced compositefilament as anchored to the part and fed past the filament drive.

Additionally and/or optionally in this fourth embodiment/aspect andoptionally other embodiments/aspects of the invention, the printingactuators and the filament drive hold the heated composite filamentironing tip at a height above the part to iron the fiber reinforcedcomposite filament as it is deposited to reshape a substantially ovalbundle of inelastic axial fiber strands within the fiber reinforcedcomposite filament to a substantially flattened block of inelasticfibers strands within a bonded rank of the part. Optionally, or inaddition, the print head and the build platen move relative to oneanother to iron the fiber reinforced composite filament by flatteningthe matrix material including the at least one axial strand with thecomposite filament ironing tip as the matrix material is melted andpulled through the composite filament ironing tip.

None of the abovementioned steps or structures in the first throughfourth embodiments and/or aspects are critical to the invention, and theinvention can be expressed as different combinations of these. Inparticular, pressing a fiber reinforced filament into a part mayoptionally be temporarily performed during threading or initializationby axial compression along the fiber composite (unmelted fiberstrand(s), partially melted and partially glass matrix), and/or by“ironing” and/or reshaping in the transverse pressure zone (e.g., printhead tip) and/or by the reshaping lip and/or by a companion “ironing”plate following the printhead. Each approach and structure is effectivein itself, and in the invention is considered in permutations andcombinations thereof. Further, the pressing may be done in combinationwith compression or tension maintained in the filament via the unmeltedfiber strands. Pressing or ironing may be done in the presence oftension upstream and downstream of the transverse pressure zone (e.g.,print head tip) and/or the ironing lip and/or companion “ironing” plate,but also or alternatively in the presence of tension downstream of thepressing and also upstream of the transverse pressure zone (e.g., printhead tip) and/or ironing lip and/or by companion “ironing” plate.

In each of these first through fourth embodiments or aspects of theinvention, as well as other embodiments or aspects thereof, optionallythe matrix material comprises a thermoplastic resin having an unmeltedelastic modulus of approximately 0.1 through 5 GPa and/or unmeltedultimate tensile strength of approximately 10 through 100 MPa, and amelted elastic modulus of less than 0.1 GPa and melted ultimate tensilestrength of less than 10 MPa, and the one or more axial fiber strandshave an elastic modulus of approximately 5-1000 GPa and an ultimatetensile strength of approximately 200-100000 MPa. These embodiments oraspects may optionally maintain a substantially constant cross sectionalarea of the fiber reinforced composite filament in clearance fit zone,the non-contact zone, the transverse pressure zone, and as a bonded rankis attached to the workpiece. In each of these first through thirdembodiments or aspects of the invention, optionally the filament has across sectional area greater than 1×10E-5 inches and less than 2×10E-3inches. Further optionally, the at least one axial strand includes, inany cross-sectional area, between 100 and 6000 overlapping axial strandsor parallel continuous axial strands. Such matrix materials includeacrylonitrile butadiene styrene, epoxy, vinyl, nylon, polyetherimide,polyether ether ketone, polyactic acid, or liquid crystal polymer, andsuch axial strand materials include carbon fibers, aramid fibers, orfiberglass.

Optionally in any of the first through fourth embodiments or aspects ofthe invention, as well as other embodiments or aspects thereof, at leastone of the feed rate and the printing rate are optionally controlled tomaintain compression in the fiber reinforced composite filament withinthe clearance fit zone. Additionally or in the alternative for these andother embodiments or aspects, optionally in a threading orinitialization phase, the filament is heated in an non-contact zoneimmediately upstream of the ironing, and the feed and printing ratescontrolled to induce axial compression along the filament within thenon-contact zone primarily via axial compressive force within the one ormore axial fiber strands extending along the filament. Additionally orin the alternative for these and other embodiments or aspects of theinvention, optionally in a threading or initialization phase, at leastone of the feed rate and the printing rate are controlled to compressthe fiber reinforced composite filament and translate an end of thefilament abutting the part laterally underneath an ironing lip to beironed by application of heat and pressure. Additionally or in thealternative for these and other embodiments or aspects of the invention,the filament is heated and/or melted by the ironing lip, and one or bothof the feed rate and the printing rate are controlled to maintainneutral to positive tension in the fiber reinforced composite filamentbetween the ironing lip and the part primarily via tensile force withinthe at least one axial fiber strand extending along the filament.

Optionally in any of the first through fourth embodiments or aspects ofthe invention, as well as other embodiments or aspects thereof,supplying is optionally via a cartridge to decouple the speed ofmanufacturing or forming the reinforced fiber material (e.g., combiningthe fiber with the matrix) from the speed of printing.

Optionally in any of the first through fourth embodiments or aspects ofthe invention, as well as other embodiments or aspects thereof, themethod may include forming a solid shell with the filament; and/or theironing lip may be rounded. Additionally or in the alternative for theseand other embodiments or aspects of the invention, the ironing lip maybe at the tip of a conduit nozzle or printing guide with across-sectional area of the conduit nozzle eyelet or outlet larger thana cross-sectional area of the conduit nozzle or printing guide inlet.Additionally or in the alternative for these and other embodiments oraspects of the invention, the cross sectional area within the walls of aheating cavity or non-contact zone is larger than a cross-sectional areaof the clearance fit zone.

Optionally in any of the first through fourth embodiments or aspects ofthe invention, as well as other embodiments or aspects thereof, the oneor more fiber cores may be constructed as a train of separate segmentsextending in an axial direction of the filament. In this case, thesegments may be located at pre-indexed locations along the axialdirection of the filament; and/or at least some of the segments mayoverlap along the axial direction of the filament. Additionally or inthe alternative for these and other embodiments or aspects of theinvention, the average length of the segments may be less than or equalto a length of the heated or non-contact zone.

Optionally in any of the first through fourth embodiments or aspects ofthe invention, as well as other embodiments or aspects thereof, thepush-pultrusion process of depositing a first filament into a layer ofmatrix material in a first desired pattern may be followed by orperformed in parallel with curing a matrix layer (e.g.,stereolithography or selective laser sintering) to form a layer of apart including the deposited first filament. Additionally or in thealternative for these and other embodiments or aspects of the invention,this alternative may optionally include cutting the first filament anddepositing a second filament in a second desired pattern in the layer ofmatrix material.

Optionally in any of the first through fourth embodiments or aspects ofthe invention, as well as other embodiments or aspects thereof, thethree dimensional printer prints structures using a substantiallyvoid-free preimpregnated (prepreg) material that remains void-freethroughout the printing process. One form of this material is areinforced filament including a core with multiple continuous strandspreimpregnated with a thermoplastic resin that has already been “wicked”into the strands, and applied using one of the push-pultrusionapproaches of the present invention to form a three dimensionalstructure. A composite formed of thermoplastic (or uncured thermoset)resin having wetted or wicked strands, may not be “green” and is alsorigid, low-friction, and substantially void free. Another form mayemploy a single, solid continuous core. Still another form may use asectioned continuous core, i.e., a continuous core sectioned into aplurality of portions along the length is also contemplated. Stillanother form may employ a solid core or multiple individual strands thatare either evenly spaced from one another or include overlaps. “Voidfree” as used herein with respect to a printing material may mean, at anupper limit, a void percentage between 1% than 5%, and at a lower limit0%, and with respect to a printed part, at an upper limit, a voidpercentage between 1 and 13%, and at a lower limit 0%. Optionally, thepush-pultrusion process may be performed under a vacuum to furtherreduce or eliminate voids.

A fiber or core “reinforced” material is described herein. The fiber orcore may either be positioned within an interior of the filament or thecore material may extend to an exterior surface of the filament, or formultistrand implementations, both. The term including “reinforced” mayoptionally extend to strands, fibers, or cores which do not provideexceptional reinforcing structural strength to the composite, such asoptical fibers or fluid conducting materials, as well as conductivematerials. Additionally, it should be understood that a core reinforcedmaterial also includes functional reinforcements provided by materialssuch as optical fibers, fluid conducting channels or tubes, electricallyconductive wires or strands.

The present invention contemplates that optionally, the entire processof push-pultrusion, including the use of different compatible materialsherein, many be a precursor or a parallel process other modes ofadditive manufacturing, in particular stereolithography (SLA), selectivelaser sintering (SLS), or otherwise using a matrix in liquid or powderform. Push-pultrusion may embed within or about parts made by these modesubstantially void free parts, enabling the entire part to exhibitenhanced strength.

If the push-pultrusion process is used to lay down bonded ranks with adominant direction or directions, these directions may optionallyexhibit anisotropic strength both locally and overall. Directionality oranisotropy of reinforcement within a structure can optionally provideenhanced part strength in desired locations and directions to meetspecific design requirements or enable lighter and/or stronger parts.

Optionally in any above-described invention, the matrix material may beacrylonitrile butadiene styrene (ABS), epoxy, vinyl, nylon,polyetherimide (PEI), Polyether ether ketone (PEEK), Polyactic Acid(PLA), or Liquid Crystal Polymer. The core or strands of the core mayreinforce structurally, conductively (electrically and/or thermally),insulatively (electrically and/or thermally), optically and/or in amanner to provide fluidic transport. The core or strands of the core mayinclude, in particular for structural reinforcing, carbon fiber, aramidor high strength nylon fiber, fiberglass. Further, multiple types ofcontinuous cores or strands may be combined in a single continuous corereinforced filament to provide multiple functionalities such as bothelectrical and optical properties.

Optionally in any above-described invention or embodiments or aspects ofthe invention, fiber reinforced composite filaments with different resinto fiber ratios may provide different properties within differentsections of the part, e.g., printed with different printheads atdifferent stages. Similarly optionally, a “low-resin” fiber reinforcedcomposite filament skeletal filler may be used for the internalconstruction to maximize the strength-to-weight ratio (e.g., 30%resin/70% fiber by cross sectional area). “Low-resin” means a resinpercentage in cross sectional area from 30% to 50%. Similarly optionallya “High-resin” fiber reinforced composite filament shell coating (e.g.,90% resin/10% fiber by cross sectional area) may be used to prevent thepossible print through of an underlying core or individual fiber strandof the core. Additionally, in some embodiments and embodiments oraspects of the invention, the consumable material may have zero fibercontent, and be exclusively resin and/or printed with conventional FFF.

All of the listed options apply individually, and in any operablepermutation or combination to each of the first, second, third, andother embodiments or aspects of the invention, including that acts orsteps are implemented with apparatus structures disclosed herein aswould be understood by one of skill in the art, and apparatus structuresperform acts or steps as disclosed herein as would be understood by oneof skill in the art. In all cases throughout the disclosure, the term“may” denotes an optional addition or alternative material, structure,act, or invention to the invention. It should be noted that discussionof a controller causing “the plurality of actuators” to move the buildplaten and/or printhead is inclusive of individually instructing anyone, two, three or more of the actuators.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A through 1D are schematic representations of a three dimensionalprinting system using a continuous core reinforced filament, in whichFIGS. 1A and 1B are schematic views of a continuous core reinforcedfilament printhead, FIG. 1C is a cross-sectional and schematic view of acompound extrusion and fiber printhead assembly, and FIG. 1D is aclose-up cross-section of a fiber printhead assembly;

FIG. 2 is a representative flow chart of a three dimensional printingprocess;

FIGS. 3A-3E are schematic representations of various embodiments of coreconfigurations of a continuous core reinforced filament 2;

FIG. 4 is a block diagram and schematic representation of a threedimensional printer capable of printing with the compound extrusion andfiber printhead assembly of FIG. 1C;

FIG. 5 is a compound timing diagram contrasting extrusion and fiberprinting control;

FIG. 6A-6C are schematic representations of conduit nozzles utilized insome embodiments of the printing system;

FIG. 7 is a schematic plan and side representation of a fiber filamentfeeding mechanism, guide tube, and cutter assembly;

FIG. 8 is a schematic representation of a three dimensional printingsystem including a cutter and a printing process bridging an open space;

FIG. 9 is a schematic representation of a part formed by thethree-dimensional printing system and/or process that includes anenclosed open space;

FIG. 10 is a schematic representation of a three-dimensional printingsystem including a guide tube;

FIG. 11 is a flowchart describing control and command execution of theprinter shown in FIGS. 1C and 5, for printing in extrusion and fibermodes as shown in FIG. 5;

FIG. 12 is a flowchart describing control and command execution of theprinter shown in FIGS. 1C and 5, for printing fiber modes as shown inFIG. 5;

FIG. 13 is a flowchart describing control and command execution of theprinter shown in FIGS. 1C and 5, for printing in extrusion mode as shownin FIG. 5;

FIGS. 14A-14C are schematic representations of nozzles and roundedoutlet nozzles respectively;

FIG. 15A is a schematic cross-sectional view of a cutter integrated witha conduit nozzle tip;

FIG. 15B is a schematic cross-sectional view of the cutter integratedwith a conduit nozzle tip depicted in FIG. 14A rotated 90°;

FIG. 15C-15D are bottom views an embodiment of a cutter integrated witha conduit nozzle tip;

FIG. 16 is a schematic cross-sectional view of a cutter integrated witha conduit nozzle tip;

FIG. 17A is a schematic representation of a three-dimensional printingsystem applying a compaction pressure during part formation;

FIG. 17B is a schematic representation of a continuous core reinforcedfilament to be utilized with the printing system prior to deposition;

FIG. 17C is a schematic representation of the continuous core reinforcedfilament and surrounding beads of materials after deposition usingcompaction pressure;

FIG. 18A is a schematic representation of a prior art extrusion nozzle;

FIG. 18B is a schematic representation of a divergent nozzle;

FIG. 18C is a schematic representation of the divergent nozzle of FIG.18B shown in a feed forward cleaning cycle;

FIG. 19A is a schematic representation of a continuous core filamentbeing printed with a straight nozzle;

FIG. 19B is a schematic representation of a green towpreg being printedwith a straight nozzle;

FIGS. 19C-19E are schematic representations of a continuous corefilament being threaded and printed with a divergent nozzle;

FIG. 20A is a schematic representation of a multi-material conduitnozzle with a low friction cold feeding zone;

FIG. 20B is a schematic representation of a slightly convergent conduitnozzle including a low friction cold feeding zone;

FIG. 21 is a schematic representation of a three dimensional printingsystem including a print arm and selectable printer heads;

FIG. 22 is a schematic representation of a three dimensional printingsystem using a continuous core reinforced filament;

FIG. 23A is a schematic representation of a semi-continuous corefilament positioned within a deposition head;

FIG. 23B is a schematic representation of a semi-continuous corefilament with overlapping strands positioned within a nozzle;

FIG. 23C is a schematic representation of a semi-continuous corefilament with aligned strands and positioned within a nozzle;

FIG. 24A is a schematic representation of a multifilament continuouscore;

FIG. 24B is a schematic representation of a semi-continuous corefilament with offset strands;

FIG. 24C is a schematic representation of a semi-continuous corefilament with aligned strands;

FIG. 24D is a schematic representation of a semi-continuous corefilament with aligned strands and one or more continuous strands;

FIG. 25 is a schematic representation of a fill pattern using asemi-continuous core filament;

FIG. 26 is a schematic representation of a stereolithography threedimensional printing process including deposited reinforcing fibers; and

FIG. 27 is a schematic representation of a stereolithography threedimensional printing process including deposited reinforcing fibers

DETAILED DESCRIPTION

In both of the relatively recent arts of additive manufacturing andcomposite lay-up, coined words have become common. For example, a“prepreg” is a pre-impregnated composite material in which a resinmatrix and a fiber assembly are prepared ahead of time as a compositeraw material. A “towpreg” is “prepreg” formed from a combination of a“tow” (a bundle of hundreds to thousands of fiber strands at very highfiber percentage, e.g., 95%) and a sticky (at room temperature) resin,conventionally being dominated by the fibers of the impregnated tow(e.g., 75% fiber strands), with the sticky resin being impregnated as ameans of transferring shear between fiber strands roughly adjacent in afilament winding process and sticking the towpreg to the rotated member.“Pultrusion” is one of the processes of making a towpreg, where a tow ispulled through a resin to form—in a process conducted entirely intension—elongated and typically hardened composites including the towembedded in the resin.

As used herein, “extrusion” shall have its conventional meaning, e.g., aprocess in which a stock material is pressed through a die to take on aspecific shape of a lower cross-sectional area than the stock material.Fused Filament Fabrication (FFF) is an extrusion process. Similarly,“extrusion nozzle” shall have its conventional meaning, e.g., a devicedesigned to control the direction or characteristics of an extrusionfluid flow, especially to increase velocity and/or restrictcross-sectional area, as the fluid flow exits (or enters) an enclosedchamber.

In contrast, the present disclosure shall use the coined word“push-pultrusion” to describe the overall novel process according to theinvention, in which unlike extrusion, forward motion of the fiberreinforced composite printing material includes a starting, threading,or initialization phase of compression followed by tension of embeddedfiber strands, as well as melted/cured and unmelted/uncured states ofthe matrix throughout the printhead as the printing material formsbonded ranks on a build table, and successively within a part. Thepresent disclosure shall also use the coined word “conduit nozzle” or“nozzlet” to describe a terminal printing head according to theinvention, in which unlike a FFF nozzle, there is no significant backpressure, or additional velocity created in the printing material, andthe cross sectional area of the printing material, including the matrixand the embedded fiber(s), remains substantially similar throughout theprocess (even as deposited in bonded ranks to the part).

As used herein, “deposition head” shall include extrusion nozzles,conduit nozzles, and/or hybrid nozzles.

The present disclosure shall also use the coined word “push-pulpreg” todescribe a material useful in push-pultrusion, which—in contrast to aconventional towpreg—the resin is preferably a thermoplastic that (i)provides sufficient friction and exposed resin material to be fed byrollers or other friction feed (ii) is sufficiently stiff (i.e., normalunmelted elastic modulus) to be pushed through a clearance fit tube orchannel without buckling in an unmelted, “glass” state, the stiffnessprovided by the embedded fiber strands and to a lesser extent theunmelted matrix resin (iii) and/or has no appreciable “tack”/moleculardiffusion in ambient conditions, i.e., is in a “glass” state in ambientor even warmed conditions so that it can be readily pushed through sucha tube without sticking.

Consolidation is typically advantageous to remove voids that result fromthe inability of the resin to fully displace air from the fiber bundle,tow, or roving during the processes that have been used to impregnatethe fibers with resin. The individually impregnated roving yarns, tows,plies, or layers of prepregs are usually consolidated by heat andpressure by compacting in an autoclave. The consolidation step hasgenerally required the application of very high pressures and hightemperatures under vacuum for relatively long times. Furthermore, theconsolidation process step using an autoclave or oven requires a“bagging” operation to provide the lay-up with a sealed membrane overthe tool to allow a vacuum to be applied for removal of air and toprovide the pressure differential necessary to effect consolidation inthe autoclave. This process step further reduces the total productivityof the composite part operation. Thus, for a thermoplastic composite itwould be advantageous to in-situ consolidate to a low void compositewhile laminating the tape to the substrate with the ATL/AFP machine.This process is typically referred to as in-situ ATL/AFP and thematerial used in that process called an in-situ grade tape.

Lastly, in the three-dimensional printing art, “filament” typicallyrefers to the entire cross-sectional area of a spooled build material,while in the composites art, “filament” refers to individual fibers of,for example, carbon fiber (in which, for example, a “1K tow” will have1000 individual strands). For the purposes of the present disclosure,“filament” shall retain the meaning from three-dimensional printing, and“strand” shall mean individual fibers that are, for example, embedded ina matrix, together forming an entire composite “filament”.

Additive manufacturing methods often result in reduced the strength anddurability versus conventional molding methods. For example, FusedFilament Fabrication results in a part exhibiting a lower strength thana comparable injection molded part, due to weaker bonding between theadjoining strips (e.g., “bonded ranks”) of deposited material (as wellas air pockets and voids.

Prepreg sheet composite construction method are time consuming anddifficult, and thereby expensive. Further, bending prepreg sheets aroundcurves may cause the fibers to overlap, buckle, and/or distort resultingin undesirable soft spots.

Feeding a commercial fiber “Towpreg” through a plastic bath to addmatrix resin, then further feeding through a custom print head does notresult in a viable additive process, due to the extremely flexible andhigh-friction (sticky) construction. Moreover, this process binds thespeed of manufacturing this composite to the speed of printing it (evenwere printing viable). Towpreg typically requires, and is sold withappropriate “tack” (a level of room-temperature adhesion sufficient tomaintain the position of the tow after it has been deposited on a toolor lay-up). Further, towpreg “green” materials tend to entrap air andinclude air voids, which are only removed by high tension and/or asubsequent vacuum and/or heating steps. These steps also slow down theprinting process.

Accordingly, there is a need for composite additive manufacturing thatis faster than lay-up or winding; that reduces or prevents entrapped airin the bonded ranks, avoiding most vacuum or heating post-processes;that provides an ability to deposit composite material in concaveshapes, and/or construct discrete features on a surface or compositeshell.

Turning now to the figures, specific embodiments of the disclosedmaterials and three dimensional printing processes are described.

FIG. 1A depicts an embodiment of a three dimensional printer 3000 inbefore applying a fiber reinforced composite filament 2 to build astructure. The fiber reinforced composite filament 2 (also referred toherein as continuous core reinforced filament) may be a push-pulpregthat is substantially void free and includes a polymer or resin 4 thatcoats or impregnates an internal continuous single core or multistrandcore 6.

The fiber reinforced composite filament 2 is fed through a conduitnozzle 10 heated (e.g., by a band heater or coil heater) to a controlledpush-pultrusion temperature selected for the matrix material to maintaina predetermined viscosity, and/or a predetermined amount force ofadhesion of bonded ranks, and/or a surface finish. In some embodiments,the filament 2 is dragged or pulled through the conduit nozzle 10 asdescribed herein. The push-pultrusion may be greater than the meltingtemperature of the polymer 4, less than a decomposition temperature ofthe polymer 4 and less than either the melting or decompositiontemperature of the core 6.

After being heated in the conduit nozzle 10 and having the matrixmaterial or polymer 4 substantially melted, the continuous corereinforced filament 2 is applied onto a build platen 16 to buildsuccessive layers 14 to form a three dimensional structure. One or bothof (i) the position and orientation of the build platen 16 or (ii) theposition and orientation of the conduit nozzle 10 are controlled by acontroller 20 to deposit the continuous core reinforced filament 2 inthe desired location and direction. Position and orientation controlmechanisms include gantry systems, robotic arms, and/or H frames, any ofthese equipped with position and/or displacement sensors to thecontroller 20 to monitor the relative position or velocity of conduitnozzle 10 relative to the build platen 16 and/or the layers 14 of thepart being constructed. The controller 20 may use sensed X, Y, and/or Zpositions and/or displacement or velocity vectors to control subsequentmovements of the conduit nozzle 10 or platen 16. For example, the threedimensional printer 1000 may include a rangefinder 15 to measuredistance to the platen 16, a displacement transducers in any of threetranslation and/or three rotation axes, distance integrators, and/oraccelerometers detecting a position or movement of the conduit nozzle 10to the build platen 16. As depicted in FIG. 1A, a (e.g., laser) rangesensor 15 may scan the section ahead of the conduit nozzle 10 in orderto correct the Z height of the conduit nozzle 10, or the fill volumerequired, to match a desired deposition profile. This measurement mayalso be used to fill in voids detected in the part. The range finder 15may measure the part after the filament is applied to confirm the depthand position of the deposited bonded ranks.

The three dimensional printer 1000 may include a cutter 8 controlled bythe controller 20 that cuts the continuous core reinforced filament(e.g., without the formation of tails) during the deposition process inorder to (i) form separate features and components on the structure aswell as (ii) control the directionality or anisotropy of the depositedmaterial and/or bonded ranks in multiple sections and layers. Asdepicted the cutter 8 is a cutting blade associated with a backing plate12 located at the conduit nozzle eyelet or outlet. Other cutters includelaser, high-pressure air or fluid, or shears.

FIG. 1A also depicts at least one secondary print head 18 optionallyemployed with the three dimensional printer 1000 to print, e.g.,protective coatings on the part including 100% resin FFF extrusion, a UVresistant or a scratch resistant coating. A description of a coupled orcompound FFF printhead 1800 may be found herein, and this descriptionapplies to protective coatings in general.

FIG. 1B depicts an embodiment of a three dimensional printer 3001 inapplying a fiber reinforced composite filament 2 to build a structure.Like numbered features are similar to those described with respect toFIG. 1A.

As depicted in FIG. 1B, upstream of a driven roller 42 and an idleroller 40, a spool (not shown) supplies under mild tension an unmeltedvoid free fiber reinforced composite filament. The filament including atleast one axial fiber strand extending within a matrix material of thefilament, having no substantial air gaps within the matrix material. Inthis example, the fiber reinforced composite filament 2 is apush-pulpreg including a nylon matrix 4A that impregnates hundreds orthousands of continuous carbon fiber strands 6A.

A “zone” as discussed herein is a segment of the entire trajectory ofthe filament from the spool (not shown) to the part. The driven roller42 and an idle roller 40 feed or push the unmelted filament at a feedrate (which is optionally variably controllable by the controller 20,not shown, and optionally is less than the printing rate, with anydifferential between these rates absorbed along the filament by a slipclutch or one-way bearing), along a clearance fit zone 3010, 3020 thatprevents buckling of filament. Within a non-contact cavity ornon-contact zone 714, the matrix material of the composite filament maybe heated. The fibers 6A within may be under axial compression at thethreading stage or beginning of the printing process, as the feeding orpushing force of the rollers 42, 40 transmits through the unmeltedmatrix to the fibers along the clearance fit zone 3010, 3020.

“Threading” is a method of pushing a pushpreg or push-pulpreg through anoutlet wherein the stiffness of the pushpreg or push-pulpreg issufficiently greater than the sticking/drag force (to prevent bucklingor flaring/jamming of the pushpreg or push-pulpreg) over the time scaleof the stitching operation. Initially, in a threading stage, the meltedmatrix material 6A and the axial fiber strands 4A of the filament 2 arepressed into the part with axial compression, and as the build platenand print head are translated with respect to one another, the end ofthe filament contacts the ironing lip 726 and is subsequentlycontinually ironed in a transverse pressure zone 3040 to form bondedranks in the part 14. Transverse pressure means pressure to the side ofthe filament, and is also discussed herein as “ironing”. As shown by thearrow, this transverse pressure zone 3040 (along with attached parts ofthe print head) may be translated adjacent to the part 14 at a printingrate (or the printing rate may be a result of translation of both oreither one of the platen 16 and print head).

The matrix material is, in this example, with respect to tensile andcompressive elastic modulus, a thermoplastic resin having an unmeltedelastic modulus of approximately 0.1 through 5 GPa and a melted elasticmodulus of less than 0.1 GPa, and the fiber strands are of a strandedmaterial having an elastic modulus of approximately 5-1000 GPa. In thismanner, the strands of fiber are sufficiently resistant to deformationto enable the entire filament to be “pushed” through limited friction insmall clearance channels, and even through free space when the matrix ismelted. With respect to tensile ultimate strength, the matrix materialis preferably a thermoplastic resin having an unmelted ultimate tensilestrength of approximately 10 through 100 MPa and a melted ultimatetensile strength of less than 10 MPa, and the at least one axial strandincludes a stranded material having an ultimate tensile strength ofapproximately 200-100000 MPa. In this manner, the internal strands offiber are sufficiently resistant to stretching or snapping to enable theentire filament to be maintained in neutral to positive (i.e., from zerotension and higher amounts of tension) tension over significantdistances extending through free space from the bonded ranks, in somecases before the matrix fully solidifies. Most filaments will have across sectional area greater than 1×10⁻⁵ (1×10E-5) inches and less than2×10⁻³ 2×10E-3 inches. In the case of multi-strand fibers, the filamentmay include, in any cross-section area, between 100 and 6000 overlappingaxial strands or parallel continuous axial strands (particularly in thecase of carbon fiber strands).

Either or both of the printing head or conduit nozzle 708 or the buildplatform 16 may be translated, e.g., the feed rate and/or the printingrate are controlled to maintain compression in the filament in thethreading stage, and to maintain neutral to positive tension in theprinting operation. The matrix material 4A of the filament 2 may beheated and melted in the non-contact zone 3030 (in particular, so thatthere is less opportunity to stick to the walls of the conduit nozzle708), but is melted or liquefied at the ironing lip or tip 726. Thelarger or diverging diameter of the non-contact zone optionally preventsthe filament from touching a heated wall 714 of the cavity defining thenon-contact zone. The feed and printing rates may be monitored orcontrolled to maintain compression, neutral tension, or positive tensionwithin the unsupported zone as well as primarily via axial compressiveor tensile force within fiber strand(s) extending along the filament.

As shown in FIGS. 1B and 1C, the transverse pressure zone 3040 includesan ironing lip 726 that reshapes the filament 2. This ironing lip 726may be a member that compacts or presses the filament 2 into the part tobecome bonded ranks. The ironing lip 726 may also receive heat conductedfrom the heated walls 714 or other heat source, in order to melt orliquefy the matrix material 4A of the filament 2 in the transversepressure zone 3040. Optionally, the ironing lip 726 in the transversepressure zone 3040 flattens the melted filament 2 on the top side,applying an ironing force to the melted matrix material and the axialfiber strands as the filament 2 is deposited in bonded ranks. This maybe facilitated by ensuring that the height of the bottom of the ironinglip 726 to the top of the layer below is less than the diameter of thefilament. Another reshaping force is applied spaced opposite of theironing lip 726 to the melted matrix material and the axial fiberstrands as a normal reaction force from the part itself. This flattensthe bonded ranks on at least two sides as the melted matrix material 4Aand the axial fiber strands 6A are pressed into the part 14 in thetransverse pressure zone 3040 to form laterally and vertically bondedranks (i.e., the ironing also forces the bonded ranks into adjacentranks).

Accordingly, the ironing lip 726 and the normal reaction force from thepart itself oppose one another and sandwich or press the meltedcomposite filament therebetween to form the bonded ranks in the part 14.The pressure and heat applied by ironing improves diffusion and fiberpenetration into neighboring ranks.

As shown in FIG. 1B, in this example, unmelted fiber reinforced filamentis cut at or adjacent the clearance fit zone 3010, 3020. It may be cut,as shown in FIG. 1A, in a gap 62 between a guide tube 72 (having aclearance fit) and the conduit nozzle 708, or may be cut within theconduit nozzle 708, e.g., upstream of the non-contact zone 3030.Alternatively or in addition, the core reinforced filament may be cut bya cutter 8 positioned at or adjacent either one of the clearance fitzone 3010, 3020 or the ironing lip 725. The clearance fit zone 3010,3020 includes an optionally interrupted channel forming a clearance fitabout the fiber reinforced composite filament 2, and this is preferablyone of a running fit or a clearance location fit, in any even sufficientclearance to permit the filament to be pushed along, even in axialcompression, without sticking and without buckling.

The pushing/feeding along the axial direction, and ironing within thetransverse pressure zone 3040 are not necessarily the only forcesforming the bonded rows. Alternatively, or in addition, the transversepressure zone 3040 and/or ironing lip 726 are translated respective tothe part 14 at a printing rate that maintains neutral to positivetension in the fiber reinforced composite filament 2 between the ironinglip 726 and the bonded ranks of the part 14, this tension being lessthan that necessary to separate a bonded rank from the part 14.

For example, after the matrix material 6A is melted by the ironing lipor tip 726, the feed and/or printing rate can be controlled by thecontroller 20 to maintain neutral to positive tension in the compositefilament 2 between the ironing lip 726 and the part 14 primarily viatensile force within the fiber strands 4A extending along the filament2. This is especially the case at the end of bonded ranks and in makinga turn to begin a new adjacent rank in the opposite direction, aspressure from the ironing lip into the part 14 may be released. This canalso be used to form bridges through open space, e.g. by drawing thefiber reinforced composite filament 2 in the transverse pressure zone3040 from a connection to a first portion of the part 14; thentranslating the transverse pressure zone 3040 through free space; thenironing to reconnect the fiber reinforced composite filament 2 to asecond portion of the part 14.

Unlike a true extrusion process, the cross sectional area of thefilament 2 is substantially maintained the entire time, and none of thestrands, the matrix, nor the filament 2 lengthens nor shortensappreciably. The feed rate of the spooled push-pulpreg and the formationrate (the printing rate) of the bonded ranks are substantially the same(although for portions of the conveyance or feeding, slip clutches orone-way bearings may permit slack, build-up or differential). At times,the feed rate and the compression rate may be temporarily anddifferentially controlled to balance sufficient neutral to positiveaxial tension downstream of the ironing lip 726, or a slip clutch may beused to allow one of feed rate or printing rate to slip. However, asubstantially constant cross sectional area of the fiber reinforcedcomposite filament is maintained in the clearance fit zone, theunsupported zone, the transverse pressure zone, and also as a bondedrank is attached to the workpiece or part 14.

FIG. 1C depicts a cross section of a compound (dual) print head with anextrusion printhead 1800 and extrusion nozzle 1802 for FFF and a fiberdeposition printhead 199 and conduit nozzle 708 for continuous fiberreinforced thermoplastic deposition. Like numbered features are similarto those described with respect to FIGS. 1A and 1B. These twocontrasting material types are not necessarily printed simultaneously,so it can be efficient to place them on the same X-Y mechanism (orX-Y-Z). This enables the two printheads 1800, 199 to share optionalcomponents both in manufacturing (e.g., commonly configured heat sinks,heater blocks, or insulation block) as well as share active componentsin operation (e.g., common cooling fans at the part-nozzle interfaceand/or for the heat sinks).

While each printhead 1800, 199 can be located independently and on itsown movement mechanism, the adjacent juxtaposition in FIG. 1Cfacilitates the following contrasting discussion.

As noted herein, the FFF process uses pressure within upstream moltenmaterial to extrude downstream molten material out of the extrusionnozzle. That is, during a print run, slice, or path segment within aslice, thermoplastic FFF extrusion, maintains the part material loadedin a reservoir 1804, 1808 in the heated zone of the print head 1800 suchthat the material therein is molten, and thereby ready to print asquickly as possible after the prior segment is complete. While thefilament is driven upstream in an unmelted temperature state, followinga sharp thermal gradient 1808 created by a thermal isolator or resistor1809 and maintained by air cooling, a reservoir 1804 of melted materialawaits driving and pressurization.

As noted herein, in contrast, the fiber reinforced thermoplasticfilament is specifically held in a non-molten position (e.g., withinTeflon tube 713) so that it can be threaded to being each segment andthen deposited. The process of “fiber force transfer” uses the stiffnessof confined fiber 2 (e.g., confined via the relatively coldthermoplastic matrix and/or small-clearance tubes at 712, 64, 72) topush/pull a fiber and resin bundle through the fiber reinforced filamentdeposition side of the print head 199. This uses axial force extendingwithin and along the non-molten strands that advance all the way throughthe tip 726 of the deposition nozzle 708, pulling the plastic resincoating with said fiber.

It is non-critical, but advantageous, to keep the fiber reinforcedfilament at ambient temperature and/or below glass transitiontemperature until it is within ½-3 cm from the ironing tip 726, i.e.,retain it upstream and out of or insulated from/isolated from any heatedzone 3040, 3030, 3035.

It is also non-critical, but advantageous, to reduce the surface area incontact or the residence time of potential filament-to-wall contact inthe last ¼-1 cm of the conduit nozzle 708 by the techniques discussedherein, e.g., to allow mostly radiant heat transfer only, employing aninner diameter of the last stage 714 of the conduit nozzle of ½-5 timesthe filament diameter, e.g., 40 thou inner diameter nozzle for 13 thoufilament, this larger inner diameter 714 being downstream of a smallerinner diameter (e.g., 32 thou at channel 712) to encourage staying awayfrom the walls of cavity 714 and avoid interior ledges that may catchthe filament 2 as it is threaded. As described herein, this is also aself-cleaning technique—wherein the pre-preg fiber embedded filamentmaterial 2 is guided to minimally touch the walls 714 of a hot conduitnozzle 708, such that the filament 2 can be threaded through withoutclogging, or peeling back fiber strands in the bundle.

It is also non-critical, but advantageous, to reduce the residence timeof potential filament-to-wall 2-to-714 contact in the last ¼-1 cm of theconduit nozzle by the techniques discussed herein, e.g., to employsufficient threading speed—e.g., 100 mm/s or higher—during threading toreduce the amount of heat transfer from any adjacent surface such as theinner diameter wall 714.

These non-critical techniques may be combined. As the conduit nozzletemperature increases above the glass transition temperature, it may beadvantageous to reduce the residence time of the composite strandfilament 2 in the conduit nozzle 708 by keeping the filament 2 upstreamin the non-heated zone, and threading the filament 2 through the conduitnozzle 708 sufficiently quickly to prevent melting of the matrix

Stationing the pre-preg continuous fiber filament 2 upstream of a hotconduit nozzle 708 when not printing, and/or using a larger diameternozzle tip 714-726, and increases the ability to push the fiber corefilament 2 through the nozzle 708 (threading), and discourages jammingor clogging, as the fiber core filament 2 do not stick to the nozzlewall 714 through adhesion and friction, and tend not to flare out whenpushed. Some melting of matrix material in the last portion 714 of theconduit nozzle 708 is tolerable, as the small inner diameters 72, 62,712 and fiber 2 may retain sufficient stiffness to thread to the part.However, this increases the likelihood of clogging.

It is non-critical, but a less advantageous alternative, to use a coldconduit nozzle 708 for threading. In this case, the temperature of theconduit nozzle 708 is reduced to below the melting point of the matrixmaterial (e.g., 40 degrees C.), and the cold filament 2 threadedtherethrough. In this case, there is no short dwell time or filamentspeed requirement in threading. Disadvantageously, the conduit nozzle708 would have to be cycled through cooling and heating steps for eachsegment printed, which could increase printing time considerably forshort-segment prints.

Continuing with reference to FIG. 1C, each of the printheads 1800 and199 are mounted on the same linear guide such that the X, Y motorizedmechanism of the printer moves them in unison. As shown, the FFFprinthead 1800 includes an extrusion nozzle 1802 with melt zone or meltreservoir 1804, a heater 1806 for heating the heater block and thenozzle. The melt reservoir 1804 continues into a high thermal gradientzone 1808, substantially formed by a thermal resistor 1809 mountedoutside the heating block. A heat sink surrounds the thermal resistor1809 to further enhance the thermal gradient. The thermal gradientseparates the melt reservoir 1804 from an unmelted zone 1810, which maybe inside the thermal resistor 1809 and/or a Teflon tube 1811. A1.75-1.8 mm or 3 mm thermoplastic filament driven through, e.g., aBowden tube provides extrusion back pressure in the melt reservoir 1804.

Parallel to, adjacent to, and of substantially the same height from thebuild platen 16, the a continuous fiber printhead 199 can be adjustedvia a flexure and set-screw mechanism to move vertically relative to theextrusion printhead 1800 while firmly restricted to move only in thevertical direction relative to the extrusion printhead 1800. Thecompanion continuous fiber embedded filament printhead 199, as shown,includes the conduit nozzle 708, the composite ironing tip 728, and thelimited contact cavity 714, in this example each within a heating blockheated by a heater 715. A cold feed zone 712 is formed within areceiving tube 64, including a capillary-like receiving tube of rigidmaterial and a small diameter (e.g. inner diameter of 32 thou)Teflon/PTFE tube extending into the nozzle 708. The cold feed zone issurrounded in this case by a PEEK insulating block 66 a and a heat sink66 b, but these are fully optional. In operation, an unattached terminalend of the fiber-embedded filament may be held in the cold feed zone,e.g., at height P1. Distance P1, as well as cutter-to-tip distance R1,are retained in a database for permitting the controller to thread andadvance the fiber-embedded filament as discussed herein. A thermalresistor, optionally of less thermal resistance than the thermalresistor 1809 of the FFF printhead 1800, cooperates with the Teflon/PTFEtube, Teflon/PEEK block 66 a, and heat sink 66 b to provide a thermalgradient marking the transition from the cold feed zone 712. Further asshown, the controller 20 is operatively connected to the cutter 8, 8A,and feed rollers 42 facing idle rollers 40.

FIG. 1D shows a schematic close-up cross section of the conduit nozzle708. As shown in FIG. 1D, and depicted essentially proportionately, theinner diameter of the receiving tube 64 (in this case, at a positionwhere a Teflon/PTFE inner tube forms the inner diameter) isapproximately 1½ to 2½ times (at, e.g., 32 thou) the diameter of thefilament 2 (at, e.g., 13 thou) shown therewithin. The inner diameter orinner width of the terminal cavity 714 (at, e.g., 40 thou (is from twoto six times the diameter of the filament 2 shown therein. These arepreferred ranges, it is considered the diameter of the receiving tubemay be from 1 1/10 to 3 times the diameter of the filament, and theinner diameter of the terminal cavity from two to 12 times the diameterof the filament. The terminal cavity is preferably of larger diameterthan the receiving tube.

In addition, as shown in essentially proportionately in FIG. 1D, theheated composite filament ironing tip 726 is moved relative to the part,at a height above the part of less than the filament diameter, to ironthe fiber reinforced composite filament as it is deposited to reshape asubstantially oval or circular bundle of inelastic axial fiber strands(labeled 2 a) within the fiber reinforced composite filament to asubstantially flattened block of inelastic fibers strands within abonded rank (labeled 2C) of the part.

Features of the compound printing head are among the inventionsdiscussed herein. For example, it is considered an optional part of thepresent invention to provide a three dimensional printer and printingprocess in which compound print heads (two or more) are provided,wherein one printing head 199 includes a composite filament ironing tip708 that irons deposited fiber with heat and pressure as discussedherein, as well as an extrusion tip 1802 that extrudes thermoplasticcompatible with the deposited fiber, but does not iron the thermoplastic(“ironing” fluidized thermoplastic is unlikely if not impossible);and/or where one printing head 199 holds filament and thermoplasticsubstantially away from the nozzle tip 726 between printing segments,and the other printing head 1800 maintains a molten thermoplasticreservoir 1804 immediately adjacent the nozzle 1802 tip between printingsegments; and/or wherein one printing head 199 employs a cutter 8 tosever the filament 2 at a known distance R1 from the tip 708 in a coldfeed zone 712 to separate one printed segment from a subsequent printedsegment, where the other printing head 1800 employs no cutter but meltsfilament near a thermal gradient 1809 to separate one segment from thesubsequent segment.

In addition or in the alternative, it is considered an optional part ofthe present invention to provide a three dimensional printer andprinting process in which compound print heads (two or more) areprovided, wherein one printing head 199 includes a terminal cavity 714having at least 4 times the volume of any partially melted or meltedthermoplastic-containing filament 2 resident therein or passingtherethrough, and thereby the filament does not substantially contact,wet, or adhere to walls of that cavity 714, where the other printinghead 1800 includes a terminal reservoir 1804 of identical volume topartially melted or melted thermoplastic-containing filament residenttherein or passing therethrough, and thereby the molten thermoplasticfully contacts, wets, and/or adheres to walls of that reservoir 1804.

In addition or in the alternative, it is considered an optional part ofthe present invention to provide a three dimensional printer andprinting process in which compound print heads (two or more) areprovided, wherein the filament feed mechanism leading to the printinghead 199 advances a continuous length filament 2 at substantiallyconstant cross-sectional area and linear feed rate substantially throughthe entire printhead 199 to deposit it to a part 14 on a build platen16, where the other print head 1800 melts and transforms, adjacent andupstream of the nozzle 1802 at the thermal gradient 1809, thecross-sectional area and linear feed rate to, e.g., for 1.75 mm supplyfilament, in the neighborhood of 10-20 times the linear feed rate (e.g.,printing at 1/15 cross sectional area of the filament), and for 3.0 mmsupply filament, in the neighborhood of 40-60 times the linear feed rate(e.g., printing at 1/50 cross sectional area of the filament).

In modification of any or all of the above, it is considered part of thepresent invention to provide a three dimensional printer and printingprocess in which compound print heads (two or more) are provided,wherein each print head 199, 1800 includes a Teflon/PTFE or otherlow-friction channel therethrough; and/or each print head 199, 1800includes a thermal resistor that provides between ½ to ⅔ of atemperature drop between the respective nozzle 708, 1802 and unmeltedzone; this thermal resistor being one of stainless steel, Hastelloy,Inconel, Incoloy, ceramic, or ceramic composite.

FIG. 2 presents a schematic flow diagram of a three dimensional printingprocess using the system and controller depicted in FIG. 1A, 1B, 1C or4. In FIG. 2, more optional steps of the invention that individually orin any combination may modify some embodiments or aspects of theinvention disclosed in FIG. 2 are denoted with dotted lines and an “A”suffix, although none of the steps shown are individually critical or inthe particular order shown, except as inherently necessary. Initially acontinuous core or multistrand fiber reinforced filament 2 is supplied(e.g., from a spool, as a push-pulpreg) at step S103. As shown in stepS103A, supplying in cartridge form can be important, as it permitscomplete independence between processes of manufacturing thepush-pulpreg and printing. That is, either manufacturing of push-pulpregor printing could be a limiting speed factor, and by using preparedcartridges or rolls of interchangeable filament, each is madeindependent. In step S105, the filament 2 is drawn from the supply orspool (e.g., by rollers) and fed in an unmelted, relatively stiff statethrough a clearance fit, or a succession of clearance fits, that mayprevent buckling of the filament as it is pushed and fed. Optionally, asshown in step S105A, during the threading or stitching process, thefilament is fed in a manner that keeps axial compression in the filament2 downstream of the feed (noting that this may change into axial neutralor positive tension in optional step S113A after the lateral pressingstep S111) into the heated conduit nozzle 708.

In step S107, the filament (and thereby the matrix material) is heatedto a desired temperature that is greater than a melting temperature ofthe resin and is less than a melting temperature of the continuous coreor strands at step S107. This completion of this step may be out oforder with respect to that shown in FIG. 2, i.e., the heating of theironing tip 726 or other heating zone may be initiated at step S107, butthe actual melting may take place only in step S11A. Moreover theheating zone may be the final zones along the path, i.e., the ironingtip or non-contact zone, as shown in optional step S107A. This stepmelts the matrix material throughout and permits the shape of thefilament to change, e.g., from a circular cross section or an oval crosssection to a square or rectangular cross section as it is packed/pressedinto the part, while nonetheless keeping a substantially similar oridentical cross sectional area. As noted in optional step S107A, thisheating may take place in or at an ironing tip 726 at the tip of theconduit nozzle. Further, within a non-contact the zone 714 or 3030, thewalls of the conduit nozzle 708 are sufficiently distant from thefilament 2 such that even heating into a plastic, glass transition ortacky form will not adhere the filament to the walls. At step S108, thecontroller 20 of the three dimensional printer 1000, 199 controls,(optionally in step S108A using the sensors described herein), position,speed, or acceleration of the conduit nozzle 708 relative to the buildplaten 16 or part, and may also monitor distances therebetween andtemperature properties at each zone or within each zone.

In step S110, while controlling the position and movement of the heatedconduit nozzle 708, the controller 20 controls the feed rate, printrate, cutter 8 and/or temperatures to maintain an axial compression inthe close fitting zone 3010 or 3020 (upstream and downstream of a cutter8) and the heating and/or non-contact zone 714, 3030 in the threadingphase, or, in the printing phase; and/or controls pressing, compressing,or flattening pressure or force within zone 3040; and/or in the printingphase controls axial neutral to positive tension within the filamentbetween the bonded ranks within the part 14 and the lateral ortransverse pressure zone 3040 and/or ironing lip 208, 508, and/or 726.

In step S111, under the control of the controller 120, the filament(matrix and fibers) 2 is pressed into the part 14. Optionally, as shownin step S11 IA, this is performed with an ironing lip or tip 208, 508,and/or 726, which may be smooth but also may be more like a doctor blade(for abrasion resistant fibers such as aramid). Simultaneously, thepressing zone 3040 and/or built platen or platform 16 are translated(optionally in 3 axes, and further optionally rotated in 3 rotationalaxes) with respect to one another at step S113. Optionally as shown byoptional step S113A, in this step S113, neutral or positive tension ismaintained and/or increased in the filament between the tip 208, 508,and/or 726 and the part 14.

In step S115, the ironing (pressing and heating) and relativetranslating (or relative printing motion for multi-axis implementations)adheres the bottom and sides of melted matrix within the filament 2 toform bonded ranks in the part 14. As discussed herein and as shown instep S115A, these ranks may optionally be tight boustrophedon ranks, maybe circular, oval, or oblate loops (e.g., racetrack shapes for longparts), may proceed with small turns in a “Zamboni” pattern, and in anyof these patterns or other patterns may be successively laid up suchthat one layer is parallel with or overlapping the layer below, or istransverse to (perpendicular or angled) to the layer below.

In step S117, after reaching the desired termination point, thecontinuous core reinforced filament may be cut. As discussed in stepsS117 and S117A, “cut” includes cutting at a position within thecompression zone 3010, 3020, in particular upstream of the conduitnozzle 8, and in particular of the filament in an unmelted, glass stateof the matrix material. “Cut” may also include cutting at a position indownstream or adjacent of the conduit nozzle 708. In addition, “cut” mayinclude, for embodiments in which the continuous strands are formed indiscrete, separated segments within the filament, pulling the conduitnozzle 708 and build platen 16 away from one another to separate thematrix material at a location where one segment of continuous fiber isadjacent the next. The controller 20 may then determine if the threedimensional part is completed. If the printing process is not completedthe controller may return to step S108 during which it senses thecurrent position and movement of the conduit nozzle prior to depositingthe next piece of continuous core reinforced filament. If the part iscompleted, the final part may be removed from the build platen.Alternatively, an optional coating may be deposited on the part using asecondary print head at S121 to provide a protective coating and/orapply a figure or image to the final part.

FIGS. 3A-3D are schematic representations of a different possiblefilaments useful with the invention, although these are not necessarilyto scale. FIGS. 3A and 3B depict cross-sections having a solidcontinuous core 6 a (e.g., a fiberglass fiber) and surroundingthermoplastic polymer 4 or resin, respectively greater than 70% resin bycross-sectional area and less than 30% resin (each by cross-sectionalarea). FIGS. 3C and 3D depict cross-sections having multi-strand fiberssurrounded by and wicked/wetted by thermoplastic resin, respectivelygreater than 60% resin and all fibers being ¼ diameter or more from theperimeter; and less than 30% resin with fibers distributed throughoutthe filament and protruding from the perimeter. FIG. 4 depicts across-section similar to FIG. 3D but including one or more separatesecondary functional strands 6 c and 6 d (with electrical, optical,thermal or fluidic conducting properties to conduct power, signals,heat, and/or fluids as well as for structural health monitoring andother desired functionalities). For carbon fiber, resin amounts forprinting in push-pulpreg manner are from 30-90% (i.e., 10-70% fiber bycross sectional area).

According to one embodiment or aspect of the invention, the polymermaterial is pre-impregnated as a push-pulpreg such that the moltenpolymer or resin wicks into the reinforcing fibers during the initialproduction of the material, optionally into the entire cross-section ofa multifilament. Optionally per this aspect of the invention, strands offiber may be pre-treated with a coating(s) or agents, such as aplasticizer, energy application by radiation, temperature, pressure, orultrasonic application to aid the polymer or resin wicking into thecross section of the multifilament core without voids. The heatingtemperature of the printing process in zone 3030 may be at a lowertemperature and/or higher viscosity of melted material than thetemperature or energy necessary to accomplish wetting, wicking, tacking,or interstitial penetration at lower viscosity to fill voids. Preparingthe push-pulpreg as a void-free prepreg permits filament width and otherproperties (e.g., stiffness, smoothness) to be predetermined, reducingthe need for complicated measurement and variable control for differentfilaments (of the same type, or of different types).

According to one embodiment or aspects of the invention, a vacuum isprovided within the heated section 714 of conduit nozzle 708 to removeair (including voids) while the matrix material is melted. Thisconstruction may be used even with filaments which may have air voidswithin (e.g., “green material”) including a solid or multifilament corewhile under vacuum. In the alternative to or in addition to the vacuumremoval of voids the present invention, the filament may be forcedthrough a circuitous path, which may be provided by offset rollers orother configurations, to mechanically work out entrapped air.

FIG. 4 depicts a block diagram and control system of the threedimensional printer which controls the mechanisms, sensors, andactuators therein, and executes instructions to perform the controlprofiles depicted in FIG. 5 and processes depicted in FIGS. 2 and 11-13.A printer is depicted in schematic form to show possible configurationsof three commanded motors 116, 118, and 120. It should be noted thatthis printer may include the compound assembly of printheads 199, 1800depicted in FIG. 1C.

As depicted in FIG. 4, the three-dimensional printer 3001 includes acontroller 20 which is operatively connected to the fiber head heater715, the fiber filament drive 42 and the plurality of actuators 116,118, 120, wherein the controller 20 executes instructions which causethe filament drive to hold an unattached terminal end of the compositefilament 2 in the cold feed zone 712 between the fiber filament drive 42and the ironing tip 726. The instructions are held in flash memory andexecuted in RAM (not shown; may be embedded in the controller 20). Anactuator 114 for applying a spray coat, as discussed herein, may also beconnected to the controller 20. In addition to the fiber drive 42, afilament feed 1830 be controlled by the controller to supply theextrusion printhead 1800. A printhead board 110, optionally mounted onthe compound printhead 199, 1800 and moving therewith and connected tothe main controller 20 via ribbon cable, breaks out certain inputs andoutputs. The temperature of the ironing tip 726 may be monitored by thecontroller 20 by a thermistor or thermocouple 102; and the temperatureof the heater block holding nozzle 1802 of any companion extrusionprinthead 1800 may be measured by a thermistor or thermocouple 1832. Aheater 715 for heating the ironing tip 726 and a heater 1806 for heatingthe extrusion nozzle 1802 are controlled by the controller 20. A heatsink fan 106 and a part fan 108, each for cooling, may be shared betweenthe printheads 199, 1800 and controlled by the controller 20.Rangefinder 15 is also monitored by the controller 20. The cutter 8actuator, which may be a servomotor, a solenoid, or equivalent, is alsooperatively connected. A lifter motor for lifting one or eitherprinthead 199, 1800 away from the part (e.g., to control dripping) mayalso be controlled. Limit switches 112 for detecting when the actuators116, 118, 120 have reached the end of their proper travel range are alsomonitored by the controller 20.

As depicted in FIG. 4, an additional breakout board 122, which mayinclude a separate microcontroller, provides user interface andconnectivity to the controller 20. An 802.11 Wi-Fi transceiver connectsthe controller to a local wireless network and to the Internet at largeand sends and receives remote inputs, commands, and control parameters.A touch screen display panel 128 provides user feedback and acceptsinputs, commands, and control parameters from the user. Flash memory 126and RAM 130 store programs and active instructions for the userinterface microcontroller and the controller 20.

FIG. 5 includes timing diagrams representative of a threading andsegment printing operation of the fiber printhead 199 and carried out,e.g., pursuant to instructions representative of the routine in FIG. 12,and comparative or companion extrusion operations of the extrusionprinthead 1800 as carried out, e.g., pursuant to instructionsrepresentative of the routine in FIG. 13 (or another extrusionprinthead). For convenience in comparison, each timing diagram carriesout the beginning of a segment to be printed in alignment at time T4(for fiber) and T34 (for extrusion), although in practice this would notbe carried out if the printheads were borne by the same actuatingassembly.

Beginning with the fiber deposition process at the top of FIG. 5, attime T0, the controller 20 commands the fiber drive 42 to advance thefiber filament 2 from its resting position (e.g., in the cold feed zone712, or adjacent the cutter 8, or both). The threading speed “T” isretained in the database in flash and/or RAM. This begins the threadingprocess. It should be noted that an initial threading process will notinclude a cut from the previous rank (shown at T6′). The threadingprocess continues while the fiber filament 2 is driven all the way tothe ironing tip 726 at time T2 at the threading speed T by the runoutdistance R1 (also stored in the database in flash and/or RAM). At thispoint, the unattached terminal end of the fiber filament 2 has reachedthe part 14 or build platen 16 itself if this is the first segment. AtT2, deposition of the fiber filament 2 beings. FIG. 5 depicts a speedtransition at T2 , i.e., a faster threading speed T than feeding speedF, but the feeding speed F may be the same, higher, or lower than thethreading speed.

More importantly, substantially simultaneously with time T2, at time T4at least one of the actuators 116, 118 is driven to begin moving thebuild platen 16 with respect to the printhead 199 at a velocity similarto that of the feeding speed F. Both actuators 116, 118 may activate inthe same or opposite directions or idle as necessary to form straight,diagonal, and curved path segments in any 2 dimensional direction. Asdetailed herein, a slipping mechanism may permit the fiber filament 2 tobe both ironed by the lip 726 and pulled from the printhead 199 whilethe fiber drive 42 slips, or the actuators 116, 118 and drive 42 may bemore actively or feedback controlled to maintain a neutral to positivetension in the fiber filament 2. T4 is preferably substantiallysimultaneous with T2, but may be slightly (e.g., one or two mm) beforeor after Tl . Each of the fiber drive 42 and active actuator(s) of 116and 118 continues to drive throughout the planned path of the fiberalong the segment being printed. A break in the timing chartaccommodates a variable length of the segment.

As the end of the segment approaches, the fiber filament 2 must besevered. Preferably, one or both of the fiber drive 42 and the activeactuator 116 and/or 118 are paused before severing, e.g., at T6 for thefiber drive 42 and at T8 for the exemplary active actuator of 116 and118. The fiber filament 2 is held between the part 14 and the fiberdrive 42 and can potentially be driven by either. The cutter 8 isactuated to quickly sever the fiber filament at T7. Subsequently, therunout distance R1 of fiber filament 2 remains in the printhead 199extending to the cutter 8, but must still be printed. Accordingly,although the fiber drive 42 does not restart after the pause (there isno need), the actuator(s) 116, 118 continue following thecontroller-directed path of the segment, again by the runout distanceR1, until the tail of the fiber filament 2 is bonded to the part 14 attime T10. It is an optional part of the invention(s) herein that atleast part of the printing and/or ironing of bonded ranks or segmentsinto the part 14 is carried out with no filament drive 42 in contactwith the filament 2 being printed. As shown in FIG. 5 by earlier timesT6′, T7′, T8′. and T′10′, a preceding segment may follow the same steps.Similarly, a following segment may follow the same steps, and/or thebuild platen 16 may be indexed down (at time T12) to begin anothersegment of another slice.

With reference to the upper part of FIG. 5, it should be noted thatwhile the threading process between T0 and T2 preferably takes placeimmediately before the segment path is started, and must take placebefore the segment path is started, the runout distance may be taken upduring idle periods. For example, immediately following T6, or any timeduring the span from T8′ through T4, the fiber drive 42 may advance thefiber at least to the end of the cold feed zone 712, to a position wherethe unattached terminal end of the fiber filament 2 may rest in anunmelted state, but more proximate the ironing lip. It an optional partof the present invention to advance fiber filament 2 along the path fromthe fiber feed 42 to a position within the cold feed zone 712 duringtimes when the actuators 116, 118 are printing and/or ironing the runoutof the severed fiber filament 2 to complete a printing segment.

With reference to the lower part of FIG. 5, extrusion printing isdifferent. When a segment is begun, at e.g. time T32, a priming pressureP (a higher feed rate) is applied for a very short time to ensure theend of the segment is level with the remainder of the segment. Theactuators 116, 118 move the printing head 1800 beginning essentiallysimultaneously with the extrusion feed at time T34. The linear advancespeed E of the thermoplastic filament advanced by the extrusion drive1830 is remarkably different from the speed of printing (e.g., 10-100times) because the pure thermoplastic filament is wholly melted andaccumulated in the reservoir 1804, and subsequently extruded through thesmall diameter nozzle 1802. At the end of a segment, at time T36 for theextrusion drive and time T40 for the actuators 116, 118 moving theprinthead 1800, the extrusion speed may be slightly reduced at time T36.However, the reservoir 1804 pressure is released primarily by the highspeed retraction of the filament by the extrusion drive 1830 at timeT38. A following segment may follow the same steps, and/or the buildplaten 16 may be indexed down (at time T42) to begin another segment ofanother slice.

As noted herein, deposition heads which guide a core reinforced filamenttherethrough with a matched velocity throughout are referred to as“conduit nozzles” whereas deposition heads which neck down and extrudeunder back pressure melted non-reinforced polymer at a higher velocitythan the supply filament are referred to as “extrusion nozzles”(according to the conventional meaning of “extrude”).

A family of straight and diverging conduit nozzles which maintain amatched velocity of the strand(s) of fiber material 6 b and the polymermatrix 4 throughout the entire conduit nozzle (at least so that thematrix does not build up within) are shown in FIGS. 6A through 6C. FIG.6A depicts a divergent conduit nozzle 200 with an increasing conduitnozzle throat diameter that matches the thermal expansion of the matrixmaterial, the conduit nozzle 200 including an inlet 202 with a diameterD1, a section with an increasing diameter 204, and an outlet 206 with adiameter D2 that is greater than the diameter D1. Alternatively, whereboth the matrix material and the fiber strand(s) have relatively lowcoefficients of thermal expansion (such as carbon fiber and LiquidCrystal Polymer), the conduit nozzle 200 may include an inlet 202 andoutlet 206 that have substantially the same diameter D3, see FIG. 6B. Aconduit nozzle 200 or 708 may also include a rounded outlet 208 or 726,as shown in FIG. 6C. For example, the rounded outlet 208 may be embodiedby an outwardly extending lip, a chamfer, a filet, an arc, or any otherappropriate geometry providing a smooth transition from the outlet,which may help to avoid fracture, applying stresses to, and/or scraping,the filament as it is printed.

FIG. 8 depicts two embodiments of a cutter for use with a threedimensional printer. Like elements described with reference to, e.g.,FIG. 1A or 1B are substantially similar. As depicted, a filament 2 or 2a, is supplied from a spool 38 and drawn and fed by driving roller 40and idle wheel 42, which apply a force directed in a downstreamdirection to the filament 2 a. Unheated, or at ambient or roomtemperature, or in any case below glass transition temperature in thiszone (3010 or 3020), the matrix of the filament 2 a is in a solid or“glass” state when this force is applied. The applied downstream force,as discussed herein, is transmitted via the glass state matrix 4A to thefiber strands 6A, which pushes the entire filament from a heated conduitnozzle 10 to build up a three dimensional part, despite that the matrixis then melted. The position of a cutter 8, 8 a, 8 b may reduce oreliminate the presence of tag-end over-runs in the final part, or permitthem to be flexibly created if advantageous.

Positioning the cutter 8 a (e.g., blade) at the outlet of the conduitnozzle 10 allows actuation of the cutter 8 a to completely cut thedeposited strip or bonded rank by severing the internal fiber strands,and/or may prevent further advance and/or dripping by physicallyblocking the conduit nozzle eyelet or outlet. A cutter 8 a or 8 benables the deposition of filament (fiber reinforced or unreinforced)with precisely controlled lengths as controlled by the controller 20. Inthe alternative, positioning a cutter 8 b upstream from the conduitnozzle 10, between the conduit nozzle 10 outlet and the feedingmechanism 40, permits a smaller gap between the conduit nozzle 10 outletand the part. In the alternative or addition, the cutter 8 b may cut thefilament while the matrix temperature is below a melting, softening, orglass transition temperature, reducing the propensity of the resin tostick to the blade which may reduce machine jamming; and/or enable moreprecise metering of the deposited material.

If a relatively close (but in no circumstances binding) fit ismaintained between the filament 2 and a guiding tube shown in FIG. 10(which may be a clearance fit 3010 or larger guide), a downstreamportion 2 b of the cut strand is pushed by the abutting upstream portion2 a is driven by the drive roller 40. The previously bonded ranks(cooled) are adhered and under tension “drag” filament 2 b from of theconduit nozzle 10 as the conduit nozzle 10 and build platen 16 are movedrelative to one another. A combination of upstream forces from thefeeding mechanism and downstream forces transferred via the unmelted orglass portion of the filament and the strands of the filament are usedto deposit the bonded ranks.

As noted, a cutter 8, 8 a, 8 b is optional, but may also preventbuckling of the material to help ensure a uniform deposition and preventmachine jams. Further, small diameter (e.g., less than 30 thou)continuous fiber filament is more susceptible to buckling. In this case,a close-fitting guide tube 10, or close-fitting guide within 64, 712 (inzones 3010, 3020) adjacent the feeding mechanism 42, 40 and/or near tothe conduit nozzle 708 outlet, may help prevent buckling of thematerial. Therefore, in one embodiment, the feeding mechanism 42, 40 maybe located within less than about 3-8 diameters from a guide tube orinlet to the nozzle. In one specific embodiment, the guide tube is around hypodermic tube. However, if the filament is shaped other thancircularly (e.g., oval, square, or tape), the guide tube is sized andshaped to match. Optionally, the filament 2 may include a smooth outercoating and/or surface where the fibers do not protrude through thefilament 2 perimeter (reducing friction or resistance within the guidetube).

In some embodiments, the three-dimensional printing system does notinclude a guide tube. Instead, the feeding mechanism may be locatedclose enough to an inlet of the nozzle, such as the receiving tube 64,such that a length of the continuous core filament 2 from the feedingmechanism to an inlet of the conduit nozzle is sufficiently small toavoid buckling. In such an embodiment, it may be desirable to limit aforce applied by the feeding mechanism to a threshold below an expectedbuckling force or pressure of the continuous core filament, or othermaterial fed into the nozzle.

In some embodiments, the maximum tension or dragging force applied tothe deposited reinforcing fibers is limited to prevent the printed partfrom being pulled up from a corresponding build plane or to provide adesired amount of neutral to positive tensioning of the continuous core.For example, a one-way locking bearing may be used to limit the draggingforce (e.g., with the speed of the feeding rollers set to be less thanthe speed of printing, but with the one-way bearing permitting thefilament to be pulled through the rollers faster than they are driven).In such an embodiment, the drive motor 42 may rotate a drive wheelthough a one-way locking bearing such that rotating the motor drives thewheel and advances material. If the material dragging exceeds the drivenspeed of the drive wheel, the one-way bearing may slip, allowingadditional material to be pulled through the feeding mechanism andnozzle, effectively increasing the feed rate to match the printing rateor head traveling speed while also limiting the driving force such thatit is less than or equal to a preselected limit. The dragging (neutralto positive tension) force may also be limited using a clutch withcommensurate built-in slip. Alternatively, in another embodiment, thenormal force and friction coefficients of the drive and idler wheels maybe selected to permit the continuous material to be pulled through thefeeding mechanism above a certain dragging force. Alternatively or inaddition, an AC induction motor, or a DC motor switched to the “off”position (e.g. a small resistance applied to the motor terminals oropening motor terminals) may be used to permit the filament to be pulledfrom the printer against motor resistance. In such an embodiment, themotors may be allowed to freewheel when a dragging force above a desiredforce threshold is applied to allow the filament to be pulled out of theprinter. In view of the above, a feeding mechanism is configured in someform or fashion such that a filament may be pulled out of the printerconduit nozzle when a dragging force applied to the filament is greaterthan a desired force threshold. Additionally, in some embodiments, afeeding mechanism may incorporate a sensor and controller loop toprovide feedback control of either a deposition speed, printer headspeed, and/or other appropriate control parameters based on thetensioning of the filament.

According to the embodiments or aspects of the invention discussedherein, the printing process may be similar in all phases, or create adifferent balance of forces within the printer, filament, and part indifferent printing phases (e.g., threading phase versus printing phase,and/or straight phases versus curved phases). For example, in oneembodiment or aspect of the invention, the printer may apply bondedranks primarily via lateral pressing and axial tension in the main,continuous printing phase, and primarily via lateral pressing and axialcompression in the threading phase where the end of the filament isfirst abutted to the platen or part and then translated under theironing tip to be melted.

According to the embodiments or aspects of the invention discussedherein, the printing system may, under axial neutral to positivetension, drag a filament 2 out of a printer conduit nozzle 708 alongstraight printed sections (and this tension extends past the conduitnozzle 708 to the feeding mechanism 42, 40 controlled at a feed rate,but which may have a slipping or clutch mechanism). During suchoperation, a printer head may be displaced or translated at a desiredrate by the controller 20, and the deposited material and/or bondedranks which are adhered to a previous layer or printing surface willapply a dragging force to the filament within the printing nozzle. Thefilament is pulled out of the printing system and deposited onto thepart 14. In contrast, in addition, or in the alternative, according tothe embodiments or aspects of the invention discussed herein, whenprinting along curves and/or corners, the feeding mechanism 42, 40 feedrate, and printing rate of the printing system may be controlled by thecontroller 20 to pushes the deposited filament onto a part or buildsurface 16. However, embodiments or aspects of the invention in which afilament is pushed out of the printing system during a straightoperation and/or where a filament is dragged out of a printer head whenprinting a curve and/or corner are also contemplated, as well asembodiments or aspects of the invention where the filament issubstantially always dragged or substantially always pushed.

The deposition of tensioned internal strand reinforced filamentsincluding a non-molten strand enables the deposited material to bepushed by the print head and adhered to the printed part at the (distal)end. The print head can suspend the filament across an open gap undertension, without the material sagging, enabling the construction ofhollow-core components (with or without the use of soluble supportmaterial).

FIG. 8 depicts free-space printing enabled by the continuous corereinforced filament. With the continuous core reinforced filament 2 battached to the part at point 44, and held by the print head at point46, it is possible to bridge the gap 48. Absent the tensioned internalfiber strands, the molten matrix material would sag and fall into thegap 48. In one example, the closed section box shown in FIG. 9 is formedby a section 50 which is bridges gap 48 and is affixed to opposingsections 52 and 54. Such free-space printing could also be used toproduce cantilever beams that cannot be printed with typical unsupportedmaterials. In such a case, optionally, a cooling mechanism such as a jetof cooling air may further prevent sagging by solidifying the polymermaterial surrounding the core, either continuously cooled over theentire or most of the build area during gap spanning, or cooled at thepoint of material advance during gap spanning. Selectively coolingmaterial only while it is over a gap may lead to better adhesion in theremaining part since maintaining an elevated enhances diffusion bondingbetween adjacent layers.

In the above noted embodiments, a cutting blade is located upstream ofthe conduit nozzle to selectively sever a continuous core when requiredby a printer. While that method is effective, there is a chance that areinforced filament will not “jump the gap” correctly between the cutterand the nozzle. Consequently, in at least some embodiments, it isdesirable to increase the reliability of retreading the core materialafter the cutting step. A cutter may be designed to reduce or eliminatethe unsupported gap after the cutting operation, e.g., a tube-shapedshear cutter in which two abutting and coaxial tubes guiding thefilament are temporarily displaced with respect to one another to shearthe filament.

FIG. 10, similar to FIGS. 1A and 1B, depicts a printer mechanism. FIG. 7is a detailed depiction of a system implementation of the cutter anddrive system shown in FIG. 10, including several components, showing thedrive roller 42 and idle roller 40, as well as the close fitting tube72, and filament 2 (which are each of very small diameter, between 10and 50 thou). Like reference numerals and parts by appearance describesimilar features. As shown in FIG. 10, the filament 2 is drawn into thefeed rollers 40, 42 under tension, and to facilitate guiding andmaintaining alignment of the filament 2 with the rollers 40, 42, thefilament 2 passes through a guide tube 74 upstream of the rollers 40,42. After passing through the rollers, 40, 42 the continuous corefilament 2 is in axial compression (at least sufficient to overcomefriction through any guiding tubes or elements). Depending on a lengthof the material under compression as well as a magnitude of the appliedforce, the continuous core filament 2 may tend to buckle. Accordingly,the continuous core filament 2 passes through a close-fitting guide tube72 (e.g., clearance fit) positioned downstream of the rollers 40, 42 andupstream of the conduit nozzle 68. The guide tube 72 both guides thefilament 2 and prevents buckling of the continuous core filament 2. Agap 62 is present between the printer head 70 and the cutter 8.

When the filament 2 is cut, the filament 2 is “rethreaded” passing fromone side of the gap 62 to the receiving guide tube 64. The receivingtube 64 itself is optionally below the glass transition temperature ofthe material. Optionally, a thermal spacer or thermal resistor 66between the receiving tube 64 and heated part of the conduit nozzle 68reduces the heat transfer to the receiving tube 64 from the hot conduitnozzle 68.

In FIG. 10, difficulty in rethreading (i.e., through the entire system,versus during the threading or stitching process through the terminalend of the printhead which initiates printing) may be encounteredbecause the filament is more flexible and prone to bending or bucklingwhen the end is unsupported, than after it has been threaded and bothends are fully supported and constrained in a first order bending mode.After the filament has been threaded, the downstream portion guides allthe subsequent filament. Cutting a filament, especially with a dull orthick blade, may also deform the end of the filament, tending toincrease misalignment of the filament 2 and the receiving tube 64.

To improve the reliability of threading the filament past the cutter 8,8 a, or 8 b, when not in use, the cutter 8 may be removed from the gap62 and the guide tube 72 is displaced (down) and/or telescoped towardsthe receiving tube 64 during rethreading. The clearance (gap) betweenthe guide tube 72 and receiving tube 64 may be reduced, or the tubes 64,72 may essentially abut the cutter 8 blade. Alternatively, pressurizedfluid, such as air, may also be directed axially down the guide tube 72,such that the axial fluid flow centers the material to align thematerial with the receiving end 16 (and may cool the guide tube 72 tubefor high-speed printing and/or higher printing temperatures, and/reducefriction of the material through the guide tube.

As shown in the upper part of FIG. 7 (plan view), the guide tube 74 maybe include a capillary tube having an inner diameter between 1½ to 2½times the diameter of the filament, and may be readily changed with achange in filament diameter and readily connected to a Bowden tube. Theclose fitting tube 72 may additionally include a similar capillary tubehaving an inner diameter between 1½ to 2½ times the diameter of thefilament 2 (optionally in combination with a flexible tube made ofTeflon/PTFE), while the receiving tube 64 may in the alternative or inaddition also include a capillary tube having an inner diameter between1½ to 3 times the diameter of the filament 2 (and may also be connectedto a similar diameter Teflon/PTFE Bowden tube). Preferably andoptionally, the capillary tube of the receiving tube 74 is a largerdiameter, especially inner diameter, than the capillary tube of theclose-fitting tube 72. As shown in FIG. 7, the driving roller 42 (andmotor) may be mounted with its slipping mechanism 43 opposite the idleroller 40 in close proximity to the cutter 8.

As shown in the lower part of FIG. 7 (side view), a cutter blade 8 f maybe a very thin sharpened or blunt blade placed at a high angle to thefilament, e.g., as shown in FIG. 7 to rotate with its supporting arm 9in such a manner that it is not pushed into the blade at a directionnormal to the filament 2, but is rapidly drawn or rotated across thefilament to slice the filament 2. The cutter 8 assembly as a wholeincludes an actuator 8 d driving the blade 8 f, the blade 8 f having athickness of less than the diameter of the unmelted fiber reinforcedcomposite filament 2, an entrance guide tube (the exemplary capillarytube of close fitting tube 72) guiding the unmelted fiber reinforcedcomposite filament 2 to the cutter blade 8 f, and an exit guide tube(the exemplary capillary tube of receiving tube 64) guiding the unmeltedfiber reinforced composite filament 2 from the cutter blade 8, whereinthe blade 8 f severs the unmelted fiber reinforced composite filament 2between the entrance guide tube 72 and the exit guide tube 64, and boththe distance between the entrance and the exit guide tubes (e.g., 7 thoubetween the tubes) and the thickness of the blade (e.g., 5 thou) areequal to or less than the diameter of the unmelted fiber reinforcedcomposite filament (e.g., 13 thou, as low as 5-8 thou). Preferably, theclearance (e.g., 1 thou) between the cutter blade 8 f and each of theentrance and exit tubes 72, 64 is less than ¼ to ½ of the thickness ofthe cutter blade 8 f, and an inner diameter of the exit guide tube 64 isgreater than an inner diameter of the entrance guide tube 72. As shownin FIG. 7 and in FIG. 1C, a linkage 8 e can provide a quick actuationand/or quick return for the servo, motor, solenoid, or other actuator ofthe cutter 8 attached to the supporting arm 9.

FIGS. 11-13 are flowcharts describing one particular implementation ofthe flowchart of FIG. 2. In particular, FIG. 12 describes a fibercomposite printing process in detail and with commonality to the timingdiagrams of FIG. 5 and the detail of FIGS. 1C and 1D, with like numbers,including step numbers, reflecting like functionality. Similar stepnumbers reflecting similar functionality but different execution orderoccur in the flow charts. FIG. 13 describes, for the purpose of contrastand coupled functionality, a FFF control process that may apply to theFFF printing head 1800 depicted in FIG. 1C. FIG. 11 describes, as acoupled functionality, control routines that may be carried out toalternately and in combination use the co-mounted FFF extrusion head1800 and fiber reinforced filament printing head 199 of FIG. 1C.

In FIG. 11, at the initiation of printing, the controller 20 determinesin step S10 whether the next segment to be printed is a fiber segment ornot, and routes the process to S12 in the case of a fiber filamentsegment to be printed and to step S14 (e.g., FIG. 13) in the case ofother segments, including e.g., base, fill, or coatings. Step S12 isdescribed in detail with reference to FIGS. 2 and 12. After each oreither of routines S12 and S14 have completed a segment, the routine ofFIG. 11 checks for slice completion at step S16, and if segments remainwithin the slice, increments to the next planned segment and continuesthe determination and printing of fiber segments and/or non-fibersegments at step S18. Similarly, after slice completion at step S16, ifslices remain at step S20, the routine increments at step S22 to thenext planned slice and continues the determination and printing of fibersegments and/or non-fiber segments. “Segment” as used herein means alinear row, road, or rank having a beginning and an end, which may beopen or closed, a line, a loop, curved, straight, etc. A segment beginswhen a printhead begins a continuous deposit of material, and terminateswhen the printhead stops depositing. A “slice” is a single layer orlaminate to be printed in the 3D printer, and a slice may include onesegment, many segments, lattice fill of cells, different materials,and/or a combination of fiber-embedded filament segments and purepolymer segments. A “part” includes a plurality of slices to build upthe part. FIG. 12's control routine permits dual-mode printing with twodifferent printheads, including the compound printheads 199, 1800 ofFIG. 1C, and using both timing approaches of FIG. 5.

FIG. 12 optionally begins with the determination that a fiber segmentwill be printed in FIG. 11's master flowchart. Initially, the threadingprocess described herein, e.g., in FIG. 5, is carried out. Before orsimultaneously with parts of the threading process (an optionallybetween steps S103, S103A and S105, S105S), the printhead 199 is indexedto a beginning printing location at step S104A and the fiber drive 42advances the fiber filament 2 to a holding position in the cold feedzone 712 (which is optionally adjacent the cutter as described hereinand as shown in step S104B, but may be in any ready position where thetemperature of the matrix material can be kept below the meltingtemperature). In preparation for step S111 of FIG. 2, at the same time,the platen is indexed in step S111B to a position below the printhead199 less than the diameter of the fiber filament 2. For example, a 13thou fiber-embedded filament 2 having a cross-sectional area of 0.08 to0.1 mm^2 may compress to a flattened row of 0.1 mm thickness and 0.9 mmwidth, so the ironing lip 726 may be arranged 0.1 mm above the previousrow. It is considered an optional part of the present invention(s)disclosed herein that a substantially round or oval fiber-embeddedfilament may be compressed, ironed, and/or flattened under heat and/orpressure to a changed shape (flattened, in some cases to a rectangularrank) and a flattened bonded rank height of less than ½ of its diameter,preferably less than ⅓ of its diameter; and a width of more than twotimes its diameter. These steps S104A, S111B, and S104B are shown to beconcurrent because they do not depend on one another, but may beconducted in any order or partly or fully simultaneously.

In step S110A, as a subset or superset of step S110 of FIG. 2, the fiberreinforced filament 2 is fed by the fiber drive 42 at a threading speed,which as described with reference to FIG. 5 is sufficient to preventenough heat transfer from the walls of the system to sick the filament 2to such walls, and until the runout distance R1 (or “cut-to-tip”distance, i.e., distance from the cutter 8 to the tip 726) is reached instep S110B. Threading is completed in this moment. Without stopping thefiber advance by the drive 42, the printhead 199 is then moved by theactuators 116, 118 to follow the programmed fiber segment path in stepS113B (additionally optionally keeping a certain tension as in stepS113A of FIG. 2). This is conducted at an ironing or printing speed,which as described with respect to FIG. 5 and the disclosure may bedifferent from threading speed of the fiber drive 42. At the same time,in step S113 the fiber feed driver 42 continues to advance the fiberfilament 2, optionally as shown in FIG. 12 and as described herein at aspeed (of linear advance of the controlling inelastic embedded fibers)less than that of the printing or ironing speed, e.g., greater than orequal to the 0.95 times the ironing speed of the printhead 199. Thefiber feed speed of FIG. S113C is optionally different or the same asthe threading speed.

As described with reference to FIG. 5, when the runout distance of R1remains to be printed, the fiber in the system needs to be severed at adistance of R1 from the ironing tip 726. Accordingly, the routine checksat step S117B whether the segment termination will occur along thesegment by a distance R1 ahead. It should be noted that the cutteractuation command can be marked at the correct time or distance alongthe segment path pursuant to runout distance R1 by path, slice, or SLTanalysis ahead of time, such that step S117B would equate to checkingfor steps S117C and S117D along the path rather than anticipating thefiber segment termination ahead. Steps S117B-S117D of FIG. 12 are asubset or superset of steps S117, S117A of FIG. 2.

When the runout distance R1 remains, the printhead actuators 116, 118and fiber filament feed drive 42 are paused at step S117C, andsubsequently, the fiber filament 2 is severed by the controller 20command to the cutter 8 actuator at step S117D. As described withreference to FIG. 5, the remainder or runout of the fiber must still belaid along the programmed segment path. Accordingly, if the plannedfiber segment S113D in the process of being printed is not complete atstep S113D, the needed actuators 116, 118 of the printhead 199 (but notnecessarily the fiber filament drive 42, which may remain paused) arerestarted and/or continued at step S113E. Steps S113D and S113E are asubset or superset of steps S113 and S113A of FIG. 2. When the fibersegment is complete, the process may return to the main printing routineto determine whether the next segment in the slice is a fiber filamentsegment. It should be noted that the routine of FIG. 12 can be performedindependently of FIG. 11 or FIG. 13, i.e., in a printer without acompound printing head 1800 of FFF type, e.g., together with the SLAtype printer of FIG. 26.

As noted, FIG. 12's control routine permits dual-mode printing, whereFIG. 13 describes the non-fiber command execution. In FIG. 13, the FFFprinthead 1800 and the platen 16 are indexed to a beginning printinglocation at step S121 and the extrusion drive 1830 quickly primes theextrusion filament, in other than a loading phase already loaded in thesystem, to increase pressure (step S123 corresponding to T32 of FIG. 5),then continues feeding to extrude. In step S125, corresponding to timeT34 of FIG. 5, the printhead 1800 moves to receive the extrusion. Instep S127, the extrusion drive 1830 continues to advance the FFFfilament to the melt reservoir 1804 at a fraction of the speed that theprinthead is moved, to create back pressure and extrude the material inthe pressurized reservoir 1804, filled with liquefied thermoplasticresin. When the segment terminates, the extrusion drive 1830 and theprinthead 1800 quickly pause at step S131, perform a retract operation(e.g., 15 mm of retract) at step S133 to release pressure in the meltreservoir and preferably create negative pressure at the nozzle 1802 tipto, e.g., prevent dripping or tailing. If called from FIG. 11, theprocess returns to the control of FIG. 11.

FIGS. 14A-14C depict a family of conduit nozzles having differentoutlets. FIG. 14A depicts a conduit nozzle 500 including an inlet 502and an outlet 504 which includes a sharp exit corner suitable for somefilaments 2 such as aramid, but which may lead to damage to fibers whichare not resistant to abrasion, such as fiberglass, carbon, plating onmetal cores, treatments to fiber optic cables. FIG. 14B depicts a smoothtransition, multiple chamfered (e.g., twice chamfered, or 45 degree)conduit nozzle eyelet or outlet 506, which reduces shear cutting offibers, and FIG. 14C depicts smoothly rounded conduit nozzle exit orironing tip 508 which reduces shearing and cutting of non-moltenstrands.

It may, in the alternative, be desirable to sever the filament 2, e.g.,by pushing a sharp edged conduit nozzle down in the vertical Zdirection, as shown by arrow 510. As depicted in FIG. 14C, the corner ofa conduit nozzle 508 may be sharpened and oriented in the Z direction tosever the continuous when forced against the filament 2 (optionallyunder tension, optionally provided by any or all of driving the feedingmechanism and/or moving the print head, or moving the build table). Asdepicted in FIGS. 15A-15D, a portion of a conduit nozzle is optionallybe sharpened and directed towards an interior of the conduit nozzleeyelet or outlet to aid in cutting material output through the conduitnozzle. As shown, smoothly chamfered conduit nozzle 600 contains afilament 2, exiting from a chamfer conduit nozzle 600, and a ring 602located at a distal outlet of the conduit nozzle. A first portion of thering 602 is non-cutting and shaped and arranged to avoid interferingwith the filament 2, and a second portion of the ring 602 includes acutting portion or blade 602 a (optionally steel, carbide, or ceramic)sharpened and oriented inwards towards the filament 2 path containedwithin the conduit nozzle 600 as seen in FIGS. 15B-15D, and occupyingless than 1/10 of the conduit nozzle eyelet or outlet area. The cuttingportion 602 a may be any of: permanently attached; selectively retractedduring printing and deployed to cut; recessed into a perimeter of theconduit nozzle eyelet or outlet; forming a part of the perimeter of theconduit nozzle exit as depicted in FIG. 15B; formed integrally with theconduit nozzle eyelet or outlet; and/or attached to the conduit nozzleeyelet or outlet.

In operation as shown in FIGS. 15A-15D, the conduit nozzle 600 istranslated in a direction D relative to a part being constructed on asurface while the filament 2 is stationary and/or held in place,resulting in the tensioning of the core material 6. As increasingtension is applied to the continuous core filament 2, the core 6 is cutthrough by the cutting portion 602 a. Alternatively, the surface and/orpart is translated relative to the conduit nozzle or the filamenttensioned using the feeding mechanism to perform the severing action.FIG. 16 presents another embodiment of a conduit nozzle tip-based cutterm the depicted embodiment, a cutting ring 604 having a sharp and edgeoriented towards the already deposited filament 2, which is actuatedrelative to the conduit nozzle 600 and part to expose the sharp edge tobring the filament in contact with the cutting element 604, and severthe core material 6.

For brittle materials, such as fiber optic cables, the cutting portion602 a or 604 may form a small score, and additional relative translationof the conduit nozzle and the part may complete the cut. For othermaterials, such as composite fibers, the rounded geometry of the conduitnozzle results in the core 6 being directed towards the cutting portion602 a or 604 under tension, with resulting consolidation (e.g.compaction) toward the cutting portion enables cutting of a large fiberwith a relatively smaller section blade. For metal fibers or ductilematerials, the cutting portion 602 a or 604 may create enough of a weakpoint in the material that sufficient tensioning of the core breaks thecore strand at the conduit nozzle exit.

The cutting portion 602 a or 604 may be a high temperature heatingelement referred to as a hot knife, which may directly or indirectlyheat the fiber to a melting temperature, carbonization temperature, or atemperature where the tensile strength of the core is low enough that itmay be broken with sufficient tensioning. The heating element may be ahigh-bandwidth heater that heats quickly and cools down quickly withoutharming the printed part; or an inductive heating element that isolatesheating to the fiber.

According to embodiments or aspects of the invention discussed herein,axial compression and/or laterally pressing the melted matrix filament 2into bonded ranks may enhance final part properties. For example, FIG.17A shows a composite fiber reinforced filament 2 applied with acompaction force, axial compression, or lateral pressure 62. Thecompaction pressure from axial compression and flattening from theironing lip 508, 726, 208 in zone 3040, compresses or reshapes thesubstantially circular cross-section filament 2 a, see FIG. 17B, intothe preceding layer below and into a second, substantially rectangularcross-section compacted shape, see FIG. 17C. The entire filament forms abonded rank (i.e., bonded to the layer below and previous ranks on thesame layer) as it is shaped. The filament 2 b both spreads and interiorstrands intrude into adjacent bonded ranks 2 c on the same layer and iscompressed into the underlying shaped filament or bonded rank ofmaterial 2 d. This pressing, compaction, or diffusion of shapedfilaments or bonded ranks reduces the distance between reinforcingfibers, and increases the strength of the resultant part (and replacesconventional techniques achieved in composite lay-up usingpost-processing with pressure plates or vacuum bagging). Accordingly, insome embodiments or aspect of the invention discussed herein, the axialcompression of the filament 2 and/or especially the physical pressing bythe printer head 70, conduit nozzle or ironing lip 508, 726, 208 in zone3040 may be used to apply a compression pressure directly to thedeposited material or bonded ranks to force them to spread or compact orflatten into the ranks beside and/or below. Cross-sectional area issubstantially or identically maintained. Alternatively or in additionunder some embodiments or aspects of the invention, pressure may beapplied through a trailing pressure plate behind the print head; a fullwidth pressure plate spanning the entire part that applies compactionpressure to an entire layer at a time; and/or heat, pressure, or vacuummay be applied during printing, after each layer, or to the part as awhole to reflow the resin in the layer and achieve the desired amount ofcompaction (forcing of walls together and reduction and elimination ofvoids) within the final part.

As noted above, and referring to FIG. 18A, nozzles 700 used in FusedFilament Fabrication (FFF) three dimensional printers typically employ aconstriction at the tip of the nozzle 700, leading to eventual cloggingand jamming of the print head (nozzle). The nozzles on most FFFthree-dimensional printers are considered wear items that are replacedat regular intervals.

In a divergent conduit nozzle according to some embodiments or aspectsof the invention, material expands as it transitions from a feed zone,to a heated melt zone, enabling any particulate matter that has enteredthe feed zone to be ejected from the larger heated zone. A divergentconduit nozzle is both easier to clean, permitting permit material to beremoved in a feed forward manner.

As used in the following discussion, “fluidly connected” is used in thecontext of a continuous connection permitting flow, and does not suggestthat the filament 2 is or is not fluid at any particular stage unlessotherwise indicated. FIG. 18B shows a conduit nozzle 708 including amaterial inlet 710, connected to a cold-feed zone 712, in turn fluidlyconnected to a heated zone 714. The cross-sectional area (perpendicularto flow direction) of the cavity or channel in the heated zone 714and/or outlet 716 is greater than the cross-sectional area(perpendicular to flow direction) of the cavity or channel located inthe cold-feed zone 712 and/or the inlet 710. The cold-feed zone 712 maybe constructed of a material that is less thermally conductive than thatof the heated zone 714, permitting the filament 2 to pass through thecold feed zone 712 and into the heated zone 714 without softening.

In one particular embodiment, the divergent conduit nozzle 708 is formedby using a low-friction feeding tube, such as polytetrafluoroethylene,fed into a larger diameter heated zone located within a conduit nozzlesuch that a portion of the heated zone is uncovered downstream from thetube. The heating zone may in addition or in the alternative beconstructed from, or coated with, a low friction material such aspolytetrafluoroethylene, and the transition from the cold feed zone 712to the heated zone 714 may be stepped, chamfered, curved, or smooth.

FIG. 18C depicts an instance where a divergent conduit nozzle 708 hasbeen obstructed by a plug 718 that has formed during use within theheated zone 714 and then removed. The divergent conduit nozzle 708 canbe cleaned using a forward-feeding cleaning cycle, e.g., starting byapplying and adhering a portion of plastic onto a print bed or cleaningarea adjacent the print bed, after which the adhered plastic is cooled(left to cool) below its melting temperature, whereupon the print bedand conduit nozzle are moved relative to each other to extract the plug718 from the conduit nozzle 708 (optionally helped by a unmeltedcompressive force from filament upstream in the feeding mechanism).While any appropriate material may be used with a divergent nozzle,nylon and nylon relatives are particularly advantageous because nylon'scoefficient of thermal expansion for nylon causes it to pull away fromthe conduit nozzle slightly during cooling and nylons exhibit a lowcoefficient of friction. Polytetrafluoroethylene walls within either orboth of the cold feed and heated zone may help with plug removal. Acleaning cycle may also be performed without the adhering step byextruding a section of plastic into free air, then removed by hand orusing an automated tool.

In the case of a straight conduit nozzle, particularly for smalldiameter filaments on the order of about 0.001″ up to 0.2″, as shown inFIG. 19A, a conduit nozzle 720 may include an inlet 724 that issubstantially the same size as conduit nozzle eyelet or outlet 722. Amaterial such as a stranded reinforced composite filament 2 passesthrough a cold feed zone 712 and into a heated zone 714 (e.g., either orboth zones low friction and/or polytetrafluoroethylene walled). Theheated zone 714 is thermally conductive, e.g., made from copper,stainless steel, brass, or the like. The filament 2 is attached to abuild platen 16 or cleaning area, and the process described with respectto FIGS. 18B and 18C carried out. Small diameter filaments are suited tothis because the low thermal mass permits them to heat up quickly and beextruded (in the case of FFF) at substantially the same size as they arefed into the print head. FIG. 19B shows a hypothetical manner in which aconventional green towpreg may come apart in a straight conduit nozzle.

FIGS. 19C-19E illustrate a method of threading according to embodimentsor aspects of the invention using a rigid push-pulpreg stranded filamentfed through a divergent conduit nozzle 708, such that clogging isreduced or eliminated. “Threading”, in this context, is the first stepin printing of continuous deposition (straight sections and rows) ofbonded ranks, and is only performed again after the filament 2 is cut,runs out, is separated, or otherwise must be again started. FIG. 19Cshows a continuous core filament 2 located within a cold feed zone 712,which may begin 5 inches or more from the heated zone 714. Where thefilament 2 has a larger thermal capacity and/or stiffness, the cold feedzone may begin closer to the heated zone 714 to provide pre-heating ofthe material prior to stitching. Within the cold feed zone 712 (below amelting temperature of the matrix), the filament 2 remains substantiallysolid and rigid, and is maintained in this position until just prior toprinting.

When printing is initiated, the filament 2 is quickly fed and threadedthrough the conduit nozzle, see FIG. 19D. The cold-feed zone 712 feedsinto the larger cavity heated zone 714, and the filament 2 isconstrained from touching the walls of the heated zone 714 by therigidity of the upstream filament still located in the cold feed zone712, see FIG. 19D. By maintaining a stiffness and preventing melting andwall contact until the material has been threaded to the outlet, fibersare prevented from peeling off, curling and/or clogging within theconduit nozzle, enabling the filament 2 to more easily pushed into andthrough the hot-melt zone 714. In some embodiments, a blast ofcompressed air may be shot through the conduit nozzle prior to and/orduring threading in order to cool the conduit nozzle to reduce thechance of sticking to the sides of the nozzle. Additionally, heating ofthe heated zone 714 of the conduit nozzle may be reduced or eliminatedduring a stitching process to also reduce the chance of sticking to thesides of the nozzle.

As feeding of the continuous core filament 2 continues, the continuouscore filament 2 contacts the build platen 16 or previous layer. Thefilament 2 is then laid or pressed along the surface by motion of theconduit nozzle relative to the build platen 16. Within a short distance,the filament 2 contacts the walls of the rounded or chamfered lip 726next to the heated zone 714 or nearly contacts the walls of the heatingzone 714, as illustrated in FIGS. 19E and 20A at or near the lip 726.Alternatively, instead of translating the printer head, the filament 2could be driven to a length longer than a length of the conduit nozzle,and when the outlet is blocked by a previous layer or by the print bed,the filament buckles to the same effect. After contacting the rounded orchamfered ironing lip 726, the wall of the heating zone 714 (or nearlycontacting the same), the continuous core filament 2 is heated to thedeposition temperature (e.g., melting temperature of the matrix) forfusing the deposited material the build platen and/or previous layers.Threading speeds may be between about 2500 mm/min and 5000 mm/min.

The rounded or chamfered lip 726 located at a distal end of the conduitnozzle eyelet or outlet 716 may provide gradual transition at theconduit nozzle eyelet or outlet may help to avoid fracturing of thecontinuous core and also applies a downward, compaction, pressing, orironing force to the continuous core filament 2 as it is deposited. Thatis, “ironing” refers to an act in which (i) a substantially lateral ortransverse force to the side of the filament (e.g., downward if thefilament is laid horizontally) is (ii) applied by a smooth surface(partially parallel to the build platen or rounded with a tangentthereof parallel to the build platen) (iii) that is translated in theprinting direction as it presses upon the melted filament to become abonded rank. The rounded or chamfered lip provides a downward force, andtranslates its lower smooth surface parallel to the build platen to ironthe continuous core filament down to the previous layer. Ironing may beconducted by positioning the lip 726 at a distance relative to adeposition surface that is less than a diameter of the continuous corefilament 2; and or by setting the height of a bonded rank to be lessthan the diameter of the filament 2, but appropriate compaction forcemay be achieved without this act (e.g., with sufficiently stiffmaterials, using the axial compression force only, positioning the lipat a distance greater than the diameter of the filament 2). Thisdistance from the lip 726 to the previous layer or build platen, or theheight of a bonded rank may be confirmed using an appropriate sensor.

The ironing and/or axial compression compaction(s) discussed herein donot require a divergent conduit nozzle. For example, the ironing orironing lip or tip 726 may be incorporated with a substantially straightconduit nozzle 720 or a slightly convergent conduit nozzle, see FIG.20A. Alternatively, or in addition, a convergent conduit nozzle may alsouse a separate cold feed zone and heated zone, e.g., as shown in FIG.20B, which shows a convergent conduit nozzle 728 including a conduitnozzle inlet 730 that feeds into a cold feed zone 712 which is in fluidcommunication with a heated zone 714 and then a convergent conduitnozzle eyelet or outlet 732.

As discussed herein, a “semi-continuous” strand composite has a corethat has been segmented along its length into a plurality of discretestrands. These discrete strands may be a single segmented strand, or aplurality of individual filaments strands bundled together butnonetheless segmented along their length. Discrete segments may bearranged such that they do not overlap. As described herein, thematerial instead of being cut, may be severed by applying a tension tothe material, in most cases while the matrix is melted or softened, andmost usefully at the termination of a printing cycle. The tension may beapplied by either backdriving a feed mechanism of the printer and/ortranslating a printer head relative to a printed part without extrudingmaterial from the nozzle.

FIG. 21 depicts an optional embodiment of a three dimensional printerwith selectable printer heads. In the depicted embodiment, a print arm1400 is capable of attaching to printer head 1402 at universalconnection 1404. An appropriate consumable material 1406, such as acontinuous core reinforced filament, may already be fed into the printerhead 1402, or it may be fed into the printer after it is attached to theprinter 1400. When another print material is desired, print arm 1400returns printer head 1402 to an associated holder. Subsequently, theprinter 1400 may pick up printer head 1408 or 1410 which are capable ofprinting consumable materials that are either different in size and/orinclude different materials to provide different.

FIG. 22 shows a three dimensional printer head 1310 used to form a partincluding a three dimensionally printed shell. The printer head 1310first deposits a series of layers 1320 (which may be fiber-reinforced orpure resin, or any combination) to build a part. The printer head 1310is capable of articulating in the traditional XYZ directions, as well aspivoting in the XT, YT and ZT directions.

FIGS. 23A-24D depict various embodiments of a semi-continuous strandcore filament being deposited from a nozzle, as contrasted to thecontinuous strand core filament 2 depicted in FIG. 24A.

Semi-continuous strands embedded in a corresponding matrix material mayalso have discrete, indexed strand lengths, where termination of thesemi-continuous core occurs at pre-defined intervals along the length ofthe filament (and the strand length may be larger than a length of themelt zone of an associated conduit nozzle). A semi-continuous strandcore might include individual strands or strand bundles arranged in3-inch (e.g., 2 to 5 inch) lengths, cleanly separated such that thefibers from one bundle abut the next bundle but do not extend into thenext bundle. A path planning algorithm controlled by the controller 20may align breaks in the strand with ends, corners, edges and otherstopping points in the print. Given a printer without a cutter and usingindexed strands cannot terminate the printing process until an indexedbreak in the semi-continuous strand is aligned with the nozzle eyelet oroutlet, the controller 20 optionally fills in areas below the minimumfeature length with resin. For example, in many geometries, the outerportion of the cross section provides more strength than the core. Insuch cases, the outer section may be printed from semi-continuousstrands up until the last integer strand will not fit in the printingpattern, at which point the remainder may be left empty, or filled withpure resin.

As depicted in FIG. 23A, a semi-continuous core filament 1000 includinga first strand 1002 and a second strand 1004 located within the matrix1006. The filament 1000 enters a cold feeding zone 712 of a conduitnozzle below the glass transition temperature of the matrix. Thefilament 1000 subsequently flows through heated or melt zone 714. Thematrix 1006 in the filament 1000 is melted within the heated zone 714prior to deposition. Upon exit from the nozzle, filament 1000 isattached to a part or build platen 16 at anchor point 1005. Severancemay occur by moving the print head forward relative to the anchor point1005, without advancing the semi-continuous core filament 1000; oralternatively the print head may remain stationary, and the upstreamsemi-continuous core filament 1000 is retracted to apply the desiredtension. The tension provided by the anchor point 1005 permits theremaining portion of the second strand 1004 located within the conduitnozzle to pull the remnant of the embedded strand from the heatednozzle.

FIGS. 23C and 24C shows an indexed semi-continuous core filament 1012where the termination of the core material is substantially complete ateach section, thereby enabling clean severance at an integer distance.The individual sections of core material are separated from adjacentsections of core material at pre-indexed locations 1016. The materialwill exhibit a reduced strength (e.g., compared to bonded ranksincluding embedded fiber) at boundary locations corresponding to thepre-indexed locations 1016 depicted in the figures. FIG. 25 illustratesthe use of such a semi-continuous core filament. As depicted in thefigure, multiple strands 1100 are deposited onto a part or build platen.The strands 1100 are deposited such that they form turns 1102 as well asother features until the print head makes it final pass and severs thematerial at 1104 as described above. Since the individual strands arelonger than the remaining distance on the part, the remaining distance1106 may either be left as a void or filled with a separate materialsuch as a polymer.

While FIG. 23A showed two individual strands, FIGS. 23B and 24B show asemi-continuous core filament 1008 including a distribution of similarlysized strands 1010 embedded in a matrix 1006. While three strands areshown in a staggered line, this is a simplified representation of arandom, or staggered, distribution of strands. For example, material mayinclude about 1,000 strands of carbon fiber (the fiber bundle termed a“1k tow”, although in the present discussion this tow must beappropriately, void-free, embedded in a thermoplastic matrix asdiscussed herein). The strands 214 may be sized and distributed suchthat there are many overlapping strands of substantially similar length.As such, a semi-continuous strand filament may include segments sizedrelative to a melt zone of a printer conduit nozzle such that theindividual strands may be pulled out of the outlet of the conduitnozzle. The melt zone could be at least as long as the strand length ofthe individual fibers in a pre-preg fiber bundle, or half as long as thestrand length of the individual fibers in a pre-preg fiber bundle.During tensioning of the material to separate the filament, the strandsembedded in a part or adhered to a printing surface provide an anchoringforce to pull out a portion of the strands remaining within the nozzle.For long strands, some strands may be retained within the nozzle, whichmay result in vertically oriented strands, optionally pushed over by theprint head, or optionally subsequently deposited layers placedstrategically as vertically oriented strands within a material layer.

A material may combine indexed and overlapping strands. For example,indexed continuous strands may be used, in parallel with smaller lengthbundles located at transition points between the longer strands, suchthat the melt zone in the conduit nozzle includes sufficient distance todrag out the overlapping strands located in the melt zone. The advantageof this approach is to reduce the weak point at the boundary between thelonger integer continuous strands. During severance of a given core andmatrix material, it is desirable that the severance force issufficiently low to prevent part distortion, lifting, upstream fiberbreaking, or other deleterious effects. In some cases, strands may bebroken during the extraction, which is acceptable at the terminationpoint. While the strand length can vary based on the application,typical strand lengths may range from about 0.2″ up to 36″ for largescale printing.

FIG. 24D shows an example of a hybrid approach between a semi-continuouscore filament and a continuous core filament. In the depictedembodiment, a material 1018 includes multiple discrete sectionsincluding one or more core segments 1014 embedded within a matrix 1006that are located at pre-indexed locations similar to the embodimentdescribed above in regards to FIGS. 24C and 25C. The material alsoincludes a continuous core 1020 embedded within the matrix 1006extending along a length of material. The continuous core 0 may be sizedsuch that it may be severed by a sufficient tensile force to enablesevering of the material at the pre-indexed locations simply by theapplication of a sufficient tensile force. Alternatively, any of thevarious cutting methods described above might also be used.

Successive layers of composite may, like traditional lay-up, be laiddown at 0°, 45°, 90°, and other desired angles to provide part strengthin multiple directions and to increase the strength-to-weight ratio. Thecontroller 20 may be controlled to functionality to deposit thereinforcing fibers with an axial alignment in one or more particulardirections and locations. The axial alignment of the reinforcing fibersmay be selected for one or more individual sections within a layer, andmay also be selected for individual layers. For example, as depicted inFIG. 26 a first layer 1200 may have a first reinforcing fiberorientation and a second layer 1202 may have a second reinforcing fiberorientation. Additionally, a first section 1204 within the first layer1200, or any other desired layer, may have a fiber orientation that isdifferent than a second section 1206, or any number of other sections,within the same layer.

Although one embodiment or aspect of the invention uses thermoplasticmatrix, hybrid systems are possible. A reinforced filament may employ amatrix that is finished by curing cycle, e.g., using heat, light,lasers, and/or radiation. For example, continuous carbon fibers areembedded in a partially cured epoxy such that the extruded componentsticks together, but requires a post-cure to fully harden. Similarly,while one embodiment or aspect of the invention use preformed continuouscore reinforced filaments, in some embodiments, the continuous corereinforced filament may be formed by combining a resin matrix and asolid continuous core in a heated extrusion nozzle. The resin matrix andthe solid continuous core are able to be combined without the formationof voids along the interface due to the ease with which the resin wetsthe continuous perimeter of the solid core as compared to the multipleinterfaces in a multistrand core. Therefore, such an embodiment may beof particular use where it is desirable to alter the properties of thedeposited material.

FIG. 26 depicts a hybrid system employing stereolithography (and/orselective laser sintering) to provide the matrix about the embeddedfiber, i.e. processes in which a continuous resin in liquid or powderform is solidified layer by layer by sweeping a focused radiation curingbeam (laser, UV) in desired layer configurations. In order to provideincreased strength as well as the functionalities associated withdifferent types of continuous core filaments including both solid andmultistrand materials, the stereolithography process associated with thedeposition of each layer can be modified into a two-step process thatenables construction of composite components including continuous corefilaments in desired locations and directions. A continuous core orfiber may be deposited in a desired location and direction within alayer to be printed, either completely or partially submerged in theresin. After the continuous fiber is deposited in the desired locationand direction, the adjoining resin is cured to harden around the fiber.This may either be done as the continuous fiber is deposited, or it maybe done after the continuous fiber has been deposited. In oneembodiment, the entire layer is printed with a single continuous fiberwithout the need to cut the continuous fiber. In other embodiments,reinforcing fibers may be provided in different sections of the printedlayer with different orientations. In order to facilitate depositing thecontinuous fiber in multiple locations and directions, the continuousfiber may be terminated using a cutter as described herein, or by thelaser that is used to harden the resin.

FIG. 26 depicts a part 1600 being built on a platen 1602 usingstereolithography. The part 1600 is immersed in a liquid resin(photopolymer) material 1604 contained in a tray 1606. During formationof the part 1600, the platen 1602 is moved by a layer thickness tosequentially lower after the formation of each layer to keep the part1600 submerged. During the formation of each layer, a continuous corefilament 1608 is fed through a conduit nozzle 1610 and deposited ontothe part 1600. The conduit nozzle 1610 is controlled to deposit thecontinuous core filament 1608 in a desired location as well as a desireddirection within the layer being formed. The feed rate of the continuouscore filament 1608 may be equal to the speed of the conduit nozzle 1610to avoid disturbing the already deposited continuous core filaments. Asthe continuous core filament 1608 is deposited, appropriateelectromagnetic radiation (e.g., laser 1612) cures the resin surroundingthe continuous core filament 1608 in a location 1614 behind the path oftravel of the conduit nozzle 1610. The distance between the location1614 and the conduit nozzle 1610 may be selected to allow the continuouscore filament to be completely submerged within the liquid resin priorto curing. The laser is generated by a source 1616 and is directed by acontrollable mirror 1618. The three dimensional printer also includes acutter 1620 to enable the termination of the continuous core filament asnoted above.

Optionally, the deposited filament is held in place by one or more“tacks”, which are a sufficient amount of hardened resin material thatholds the continuous core filament in position while additional corematerial is deposited. As depicted in FIG. 27, the continuous corefilament 1608 is tacked in place at multiple discrete points 1622 by thelaser 1612 as the continuous core filament is deposited by a nozzle, notdepicted. After depositing a portion, or all, of the continuous corefilament 1608, the laser 1612 is directed along a predetermined patternto cure the liquid resin material 1604 and form the current layer.Similar to the above system, appropriate electromagnetic radiation(e.g., laser 1612), is generated by a source 1616 and directed by acontrollable mirror 1618. The balance of the material can be cured tomaximize cross linking between adjacent strands is maximized, e.g., whena sufficient number of strands has been deposited onto a layer andtacked in place, the resin may be cured in beads that are perpendicularto the direction of the deposited strands of continuous core filament.Curing the resin in a direction perpendicular to the deposited strandsmay provide increased bonding between adjacent strands to improve thepart strength in a direction perpendicular to the direction of thedeposited strands of continuous core filament. If separate portions ofthe layer include strands of continuous core filament oriented indifferent directions, the cure pattern may include lines that areperpendicular or parallel to the direction of the strands of continuousfibers core material in each portion of the layer.

To avoid the formation of voids along the interface between thecontinuous core filament and the resin matrix during thestereolithography process, it may be desirable to facilitate wetting orwicking. Wetting of the continuous fiber and wicking of the resinbetween the into the cross-section of the continuous multistrand coremay be facilitated by maintaining the liquid resin material at anelevated temperature, for a certain amount of time, using a wettingagent on the continuous fiber, applying a vacuum to the system, or anyother appropriate method.

In addition to using the continuous core reinforced filaments to formvarious composite structures with properties in desired directions usingthe fiber orientation, in some embodiments it is desirable to provideadditional strength in directions other than the fiber direction. Forexample, the continuous core reinforced filaments might includeadditional composite materials to enhance the overall strength of thematerial or a strength of the material in a direction other than thedirection of the fiber core. For example, carbon fiber core material mayinclude substantially perpendicularly loaded carbon nanotubes. Loadingsubstantially perpendicular small fiber members on the core increasesthe shear strength of the composite, and advantageously increases thestrength of the resulting part in a direction substantiallyperpendicular to the fiber direction. Such an embodiment may help toreduce the propensity of a part to delaminate along a given layer.

The composition of the two polymer matrix binders used in the internalportion and outer coating of a composite filament may differ by one ormore of the following factors: polymer molecular weight, polymer weightdistribution, degree of branching, chemical structure of the polymerchain and polymer processing additives, such as plasticizers, meltviscosity modifiers, UV stabilizers, thermal stabilizers, opticalbrighteners, colorants, pigments or fillers.

In another embodiment, it is desirable to increase the bonding strengthwith a build platform to help prevent lifting off of a part, or sectionof a part, from the build platform. Consequently, in some embodiments, asurface energy modifier is applied to the build platform to facilitatethe adhesion of the extruded filament to said platform. In someembodiments, the noted adhesion modification is used to increase theadhesion of the first bonding layer to the build platform in a few keyareas, such as the corners of a box, thereby causing greater adhesionwhere the part is most likely to peel up from the platform. The centerof the box, however, may be substantially free of surface energymodifiers to facilitate easy removal.

In some embodiments, a continuous core, such as continuous carbonfibers, is combined with a semi-aromatic polyamides and/or asemi-aromatic polyamide blends with linear polyamides which exhibitexcellent wetting and adhesion properties to the noted continuous carbonfibers. Examples of such semi-aromatic polyamides include blends ofsemi-aromatic and linear polyamides from EMS-Grivory, Domat/Ems,Switzerland, such as Grivory HT1, Grivory HT2, Grivory HT3 and othersimilar blends. By combining continuous reinforced fiber towpregs withhigh-temperature melting and fiber wetting polyamides and their blends,parts may be manufactured which are characterized by exceptionalmechanical strength and long-term temperature stability at usetemperatures 120 degrees C. and higher while ensuring extrudability ofthe composite tow, excellent fiber-matrix wettability, complete fibertowpreg permeation with the resin and excellent shear strength at thefiber-matrix interface.

Appropriate rheological pretreatments of a continuous core include theuse of a low viscosity or high melt flow index resins or polymer melts.Additionally, polymers exhibiting low molecular weights and/or linearchains may be used. Polymers exhibiting a sharp melting point transitionwith a large change in viscosity might also be used. Such a transitionis a typical property exhibited by polyamides.

Appropriate fiber wetting pretreatments may include precluding the fibersurfaces with a very thin layer of the same or similar polymer from adilute polymer solution followed by solvent evaporation to obtain alike-to-like interaction between the melt and the fiber surface. Polymeror resin solutions in neutral and compatible solvents can haveconcentrations from about 0.1 wt.-% to 1 wt.-% or higher. Additionally,one or more surface activation methods may be used to introduce orchange the polarity of the fiber surface and/or to introduce chemicallyreactive surface groups that would affect wetting/impregnation (contactangle) and adhesion (matrix-fiber interfacial shear strength) byphysically or chemically bonding the polymer matrix with the fibersurface. The fiber surface may also be chemically activated using:activation methods in gas and liquid phase, such as silanization in thepresence of hexamethyldisilizane (HMDS) vapors, especially at elevatedtemperatures; and solvent-phase surface modification using organosiliconor organotitanium adhesion promoters, such astris(ethoxy)-3-aminopropylsilane, tris(ethoxy)glycidyl silane,tetraalkoxytitanates and the like.

It should be noted that specific measurements given herein may have thefollowing approximate SI equivalents.

Imperial SI Imperial SI “5-8 thou” = 0.1-0.2 mm “1-2 thou” = 0.025 to0.05 mm 0.005″-0.008″ 0.001″-0.002″ “63 thou” = 1.6 mm “40 thou” = 1.0mm 0.063″ (1.2-2.0 mm) 0.040″ (0.8-1.2 mm) “13 thou” = 0.3-0.4 mm “28thou” = 0.7 mm 0.013″ 0.028″ (0.6-0.8 mm) “50 thou” = 1.2-1.4 mm “32thou”-0.032″ 0.8 mm 0.050″ (0.7-0.9 mm)

What is claimed is:
 1. A three-dimensional printer for additivemanufacturing of a part, the three dimensional printer comprising: afiber composite filament supply of unmelted fiber reinforced compositefilament including one or more inelastic axial fiber strands extendingwithin a matrix material of the filament; a movable build platen forsupporting the part; a print head opposing the build platen andincluding a composite filament ironing tip and a heater that heats thecomposite filament ironing tip above a melting temperature of the matrixmaterial; a plurality of actuators that move the print head and thebuild platen relative to one another in three degrees of freedom; afilament drive that drives the unmelted fiber reinforced compositefilament, and the inelastic fiber strands embedded within, into theprint head at a linear feed rate; a cold feed zone positioned betweenthe filament drive and the ironing tip, maintained below a meltingtemperature of the matrix material; and a controller operativelyconnected to the heater, the filament drive and the plurality ofactuators, wherein the controller executes instructions which cause thefilament drive to hold an unattached terminal end of the compositefilament in the cold feed zone between the filament drive and theironing tip.
 2. The three-dimensional printer according to claim 1,wherein the controller further executes instructions which cause thefilament drive to advance the unattached terminal end of the compositefilament through the print head and to the heated composite filamentironing tip without stopping, such that the unattached terminal endadvances at least at the current feeding rate as it passes throughlocations having a temperature sufficient to melt the matrix material ofthe filament.
 3. The three-dimensional printer according to claim 2,wherein the controller further executes instructions which cause thefilament drive to advance the unattached terminal end of the compositefilament through the print head and to the heated composite filamentironing tip at a speed sufficient to prevent the unattached terminal endfrom receiving sufficient heat transfer to adhere to interior walls ofthe print head adjacent the composite filament ironing tip.
 4. Thethree-dimensional printer according to claim 3, wherein the controllerfurther executes instructions which cause the filament drive to advancethe unattached terminal end of the composite filament through the printhead and to the heated composite filament ironing tip at a speed of 100mm/s.
 5. The three-dimensional printer according to claim 1, wherein thecontroller further executes instructions which cause the filament driveto advance the unattached terminal end of the composite filament throughthe print head, to the heated composite filament ironing tip, and beyondthe heated composite filament ironing tip without stopping.
 6. Thethree-dimensional printer according to claim 5, wherein the controllerfurther executes instructions which cause the plurality of actuators tobegin moving the print head and the build platen relative to one anotherin at least one degree of freedom substantially at the moment thefilament drive advances the unattached terminal end of the compositefilament to the heated composite filament ironing tip.
 7. Thethree-dimensional printer according to claim 1, wherein the controllerfurther executes instructions which cause the filament drive to advanceuntil the terminal end and at least a portion of the one or moreinelastic axial fiber strands are anchored within a part on the buildplaten.
 8. The three-dimensional printer according to claim 1, furthercomprising a cutter positioned between the filament drive and theironing tip, wherein the controller further executes instructions whichcause the cutter to sever the unmelted fiber reinforced compositefilament within the cold feed zone.
 9. The three-dimensional printeraccording to claim 8, wherein the controller further executesinstructions which, subsequent to severing the unmelted fiber reinforcedcomposite filament cause the plurality of actuators to drag remainingunmelted fiber reinforced composite filament from the print head throughthe cold feed zone and the composite filament ironing tip.
 10. Thethree-dimensional printer according to claim 8, wherein the controllerfurther executes instructions which, subsequent to severing the unmeltedfiber reinforced composite filament, causes the filament drive to holdthe unattached terminal end of the unmelted fiber reinforced compositefilament in the cold feed zone adjacent the cutter.
 11. Thethree-dimensional printer according to claim 8, further comprising adatabase including a value representing a runout distance between thecutter and the composite filament ironing tip, wherein the controllerfurther executes instructions which cause the plurality of actuators andthe filament drive to substantially simultaneously pause, cause thecutter to then sever the unmelted fiber reinforced composite filamentduring said pause, and causes the plurality of actuators to resumemovement of the print head and the build platen relative to one anotheralong at least one degree of freedom for at least the runout distance tocomplete bonding the remainder of the fiber reinforced compositefilament.
 12. The three-dimensional printer according to claim 8,further comprising a database including a value representing a runoutdistance between the cutter and the composite filament ironing tip,wherein the controller further executes instructions which cause thefilament drive to advance the unmelted fiber reinforced compositefilament by the runout distance before causing the plurality ofactuators and the filament drive to substantially simultaneously drivealong at least one common degree of freedom at a substantially commonspeed of advance of the inelastic axial fiber strands within the fiberreinforced composite filament as anchored to the part and fed past thefilament drive.
 13. The three-dimensional printer according to claim 1,further comprising a cutter positioned between the filament drive andthe ironing tip, wherein the controller further executes instructionswhich cause the cutter to sever the unmelted fiber reinforced compositefilament prior to holding the unattached terminal end of the unmeltedfiber reinforced composite filament in the cold feed zone between thefilament drive and the ironing tip.
 14. The three-dimensional printeraccording to claim 1, further comprising a cutter positioned between thefilament drive and the ironing tip, the cutter comprising: an actuatordriving a blade, the blade having a thickness of less than the diameterof the unmelted fiber reinforced composite filament, an entrance guidetube guiding the unmelted fiber reinforced composite filament to thecutter, and an exit guide tube guiding the unmelted fiber reinforcedcomposite filament from the cutter, wherein the blade severs theunmelted fiber reinforced composite filament between the entrance guidetube and the exit guide tube, and both the distance between the entranceand the exit guide tubes and the thickness of the blade are equal to orless than the diameter of the unmelted fiber reinforced compositefilament.
 15. The three-dimensional printer according to claim 14,wherein the clearance between the cutter and each of the entrance andexit tubes is less than ¼ to ½ of the thickness of the cutter, andwherein an inner diameter of the exit guide tube is greater than aninner diameter of the entrance guide tube.
 16. The three-dimensionalprinter according to claim 1, wherein the controller further executesinstructions which cause the plurality of actuators to move a partanchoring a continuously embedded inelastic fiber extending from thepart through the print head to the filament drive at a printing ratesubstantially equal to or greater than the feeding rate at which thefilament drive advances unmelted fiber reinforced composite filament andthe inelastic fiber embedded therein.
 17. The three-dimensional printeraccording to claim 1, further comprising a clutch, wherein the clutchpermits the filament drive to slip to accommodate a difference in theprinting rate and the feeding rate.
 18. The three-dimensional printeraccording to claim 1, further comprising a clearance fit channel withinthe cold feed zone having an inner diameter between 1½ and 2½ times thediameter of the unmelted fiber reinforced composite filament, whichguides the filament along a path or trajectory and/or prevents bucklingof the filament.
 19. The three-dimensional printer according to claim18, wherein an interior diameter of the print head between the clearancefit channel and the composite filament ironing tip is from two to sixtimes the diameter of the unmelted fiber reinforced composite filament,sufficient to prevent the unattached terminal end from receivingsufficient heat transfer to adhere to interior walls of the print headadjacent the composite filament ironing tip.
 20. The three-dimensionalprinter according to claim 1, further comprising a clearance fit channelwithin the cold feed zone which guides the filament along a path ortrajectory and/or prevents buckling of the filament, and wherein aninterior diameter of the print head between the clearance fit channeland the composite filament ironing tip is from larger than the interiordiameter of the clearance fit channel.
 21. The three-dimensional printeraccording to claim 1, wherein the controller further executesinstructions which cause the plurality of actuators and the filamentdrive to cooperate to maintain a transverse pressure zone that bothpresses and melts fiber reinforced composite filament to form the parton the build platen as the build platen and printhead are moved relativeto one another.
 22. The three-dimensional printer according to claim 21,wherein the controller further executes instructions which cause theplurality of actuators and the filament drive to cooperate to apply acompressive force along the inelastic axial strands of the filament. 23.The three-dimensional printer according to claim 1, wherein thecontroller further executes instructions which cause the plurality ofactuators and the filament drive to apply an ironing force, using asurface of the heated composite filament ironing tip, to the side of themelted matrix filament to form the part on the build platen.
 24. Thethree-dimensional printer according to claim 1, wherein the controllerfurther executes instructions which cause the plurality of actuators toapply a neutral to positive tension force along the embedded inelasticfiber and between a part anchoring an embedded inelastic fiber and theheated composite filament ironing tip.
 25. The three-dimensional printeraccording to claim 24, wherein the neutral to positive tension force isa less than that necessary to separate a bonded rank from the part. 26.The three-dimensional printer according to claim 1, wherein thecontroller controls the filament drive to not retract the filamentpreceding and following the deposition of a fiber reinforced compositefilament to form a bonded rank.
 27. The three-dimensional printeraccording to claim 1, wherein the controller further executesinstructions which cause the plurality of actuators and the filamentdrive to hold the heated composite filament ironing tip at a heightabove the part to iron the fiber reinforced composite filament as it isdeposited to reshape a substantially oval bundle of inelastic axialfiber strands within the fiber reinforced composite filament to asubstantially flattened block of inelastic fibers strands within abonded rank of the part.
 28. The three-dimensional printer according toclaim 1, further comprising a cutter positioned adjacent the compositefilament ironing tip, wherein the controller further executesinstructions which cause the cutter to sever the composite filamentadjacent the composite filament ironing tip.
 29. The three-dimensionalprinter according to claim 1, wherein the controller further executesinstructions which cause the plurality of actuators that move the printhead and the build platen relative to one another and the filament driveto pull the filament through the composite filament ironing tip and tomaintain tension along the at least one axial strand while the matrixmaterial is at least partially melted and unable to transmit tensionforce.
 30. The three-dimensional printer according to claim 1, whereinthe controller further executes instructions which cause the pluralityof actuators that move the print head and the build platen relative toone another and the filament drive to translate the composite filamentironing tip and the part with respect to one another to iron the fiberreinforced composite filament by flattening the matrix materialincluding the at least one axial strand with the composite filamentironing tip as the matrix material is melted and pulled through thecomposite filament ironing tip.
 31. The three-dimensional printeraccording to claim 1, wherein the matrix material comprises athermoplastic resin having an unmelted ultimate tensile strength ofapproximately 10 through 100 MPa and a melted ultimate tensile strengthof less than 10 MPa, and the at least one axial strand includes astranded material having an ultimate tensile strength of approximately200-100000 MPa.
 32. The three-dimensional printer according to claim 1,wherein the filament has a cross sectional area greater than 1×10E-5square inches and less than 2×10E-3 square inches,
 33. 33. Thethree-dimensional printer according to claim 1, wherein the at least oneaxial strand includes, in any cross-section area, between 100 and 6000parallel continuous axial strands.
 34. The three-dimensional printeraccording to claim 1, wherein the controller further executesinstructions which cause the plurality of actuators that move the printhead and the build platen relative to one another and the filament driveto control the height of the composite filament ironing tip from the topof the part to be less than a diameter of the filament.
 35. Thethree-dimensional printer according to claim 1, wherein the matrixmaterial comprises a thermoplastic resin having an unmelted elasticmodulus of approximately 0.1 through 5 GPa and a melted elastic modulusof less than 0.1 GPa, and the at least one axial fiber strand includes astranded material having an elastic modulus of approximately 5-1000 GPa.36. The three-dimensional printer according to claim 1, wherein thecontroller further executes instructions that cause the plurality ofactuators that move the print head and the build platen relative to oneanother and the filament drive to control at least one of the feed rateand the printing rate to compress the fiber reinforced compositefilament and translate an end of the filament abutting the partlaterally underneath the composite filament ironing tip to be ironed byapplication of heat and pressure.
 37. The three-dimensional printeraccording to claim 1, wherein the controller further executesinstructions that cause the plurality of actuators that move the printhead and the build platen relative to one another and the filament driveto press the melted matrix material and the at least one axial fiberstrand into the part to form laterally and vertically bonded ranks, andflatten the bonded ranks on at least two sides by applying an ironingforce to the melted matrix material and the at least one axial fiberstrand with the composite filament ironing tip, and applying an opposingreshaping force to the melted matrix material and the at least one axialfiber strand as a normal reaction force from the part itself.
 38. Thethree dimensional printer of claim 1, wherein the matrix material of thefilament is formed from one of semi-aromatic polyamides, andsemi-aromatic polyamide blends with linear polyamides.
 39. The threedimensional printer of claim 1, wherein the filament has an outerdiameter of that is greater than or equal to 0.006 inches and less thanor equal to 0.030 inches, and where the number of strands in across-sectional area is approximately 300-1000 strands.